build: migrate to androidx

* use androidx support library
* update gradle
* update dependencies

Change-Id: Iba7a2734e783a4ce0d5e6459dc33b9036e46d2a5
diff --git a/ring-android/app/src/main/res/layout/frag_share.xml b/ring-android/app/src/main/res/layout/frag_share.xml
index 8d37e81..d6ff163 100644
--- a/ring-android/app/src/main/res/layout/frag_share.xml
+++ b/ring-android/app/src/main/res/layout/frag_share.xml
@@ -10,7 +10,7 @@
         android:layout_alignParentBottom="true"
         android:background="@color/color_primary_dark">
 
-        <android.support.v7.widget.AppCompatButton
+        <androidx.appcompat.widget.AppCompatButton
             android:id="@+id/share_button"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"