Make FloatingActionButton overlap LinearLayout

Follow the image of how it was and the code.   I put your 1st RelativeLayout inside another RelativeLayout

<?xmlversion="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawerLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/colorBackgroud"
android:fitsSystemWindows="true"
app:itemIconTint="@color/textColorPrimary"
tools:openDrawer="start">

<RelativeLayout

    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >
        <LinearLayout
            xmlns:tools="http://schemas.android.com/tools"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            tools:context=".activity.MainActivity">

            <include
                android:id="@+id/toolbar"
                layout="@layout/toolbar"
                android:layout_height="85dp"
                tools:ignore="IncludeLayoutParam" />

        </LinearLayout>


        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:layout_alignParentBottom="true"
            android:background="@color/colorAccent"
            android:elevation="10dp"
            android:orientation="horizontal">


        <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:orientation="horizontal">

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:orientation="horizontal"
                    android:padding="10dp">

                    <ImageView
                        android:layout_width="22dp"
                        android:layout_height="match_parent"
                        android:src="@drawable/ic_message" />

                    <TextView
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="center"
                        android:layout_marginLeft="12dp"
                        android:gravity="start"
                        android:text="Mensagens"
                        android:textColor="@color/textColorPrimary"
                        android:textSize="22sp" />
                </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="horizontal">

                <ImageView
                    android:layout_width="22dp"
                    android:layout_height="match_parent"
                    android:src="@drawable/ic_bookmark" />

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:layout_marginLeft="12dp"
                    android:gravity="start"
                    android:text="Itens salvos"
                    android:textColor="@color/textColorPrimary"
                    android:textSize="22sp" />
            </LinearLayout>

            </LinearLayout>

        </LinearLayout>


    </RelativeLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_marginBottom="30dp"
        android:layout_marginRight="20dp"
        android:backgroundTint="@color/colorPrimary"
        android:src="@drawable/ic_border_color"
        android:tint="@color/textColorSecondy" />

</RelativeLayout>

<android.support.design.widget.NavigationView
    android:id="@+id/navView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:background="@color/colorBackgroud"
    app:headerLayout="@layout/nav_header"
    app:itemIconTint="@color/textColorPrimary"
    app:itemTextColor="@color/textColorPrimary"
    app:menu="@menu/menu_nav">

</android.support.design.widget.NavigationView>

Pass the Floating Action Button code to before

</android.support.v4.widget.DrawerLayout>

Even at the end of the file, you should solve the problem, if it does not resolve the elevation override and put it above 8dp