downgrade alpha libraries (#1273)

app/build.gradle

@@ -98,10 +98,10 @@ dependencies {
     implementation 'androidx.browser:browser:1.0.0'
     implementation 'androidx.recyclerview:recyclerview:1.0.0'
     implementation 'androidx.legacy:legacy-support-v13:1.0.0'
-    implementation 'com.google.android.material:material:1.1.0-alpha06'
+    implementation 'com.google.android.material:material:1.1.0-alpha05'
     implementation 'androidx.exifinterface:exifinterface:1.0.0'
     implementation 'androidx.cardview:cardview:1.0.0'
-    implementation 'androidx.preference:preference:1.1.0-alpha05'
+    implementation 'androidx.preference:preference:1.1.0-alpha04'
     implementation 'com.squareup.retrofit2:retrofit:2.5.0'
     implementation 'com.squareup.retrofit2:converter-gson:2.5.0'
     implementation 'com.squareup.retrofit2:adapter-rxjava2:2.5.0'

app/src/main/res/drawable/background_main_toolbar.xml

@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-    android:shape="rectangle">
-    <solid android:color="?android:colorBackground" />
-</shape>

app/src/main/res/layout/activity_main.xml

@@ -33,7 +33,7 @@
             android:layout_alignParentTop="true"
             android:layout_alignParentEnd="true"
             android:layout_toEndOf="@id/drawer_toggle"
-            android:background="@drawable/background_main_toolbar"
+            android:background="?android:colorBackground"
             android:elevation="@dimen/actionbar_elevation"
             app:tabGravity="fill"
             app:tabIconTint="@color/tab_icon_color"