Bump version to 2.2.20-beta and update fastlane metadata

fastlane/metadata/android/en-US/changelogs/78.txt

+## Fixed
+* Crash on network change if app is in background on API 24+ (#980)

mobile/build.gradle

@@ -31,8 +31,8 @@ android {
         applicationId "org.openhab.habdroid"
         minSdkVersion 14
         targetSdkVersion 27
-        versionCode 77
-        versionName "2.2.19-beta"
+        versionCode 78
+        versionName "2.2.20-beta"
         multiDexEnabled true
         testInstrumentationRunner 'android.support.test.runner.AndroidJUnitRunner'
     }