Begin development on verison 4.2.1

Change-Id: I61703a8af888e0cdb501957c77532b4def8aaba7

Author: samtstern

buildSrc/src/main/kotlin/Config.kt

@@ -1,5 +1,5 @@
 object Config {
-    const val version = "4.2.0"
+    const val version = "4.2.1-SNAPSHOT"
     val submodules = listOf("auth", "auth-github", "common", "firestore", "database", "storage")
 
     private const val kotlinVersion = "1.2.61"