Bump version to 3.28.4

// FREEBIE

AndroidManifest.xml

@@ -2,8 +2,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           xmlns:tools="http://schemas.android.com/tools"
           package="org.thoughtcrime.securesms"
-      android:versionCode="231"
-      android:versionName="3.28.3">
+      android:versionCode="232"
+      android:versionName="3.28.4">
 
     <uses-sdk tools:overrideLibrary="com.amulyakhare.textdrawable,com.astuetz.pagerslidingtabstrip,pl.tajchert.waitingdots,com.h6ah4i.android.multiselectlistpreferencecompat,android.support.v13,com.davemorrissey.labs.subscaleview"/>