added mavenCentral() for gradle builds

As jCenter is shutting down so adding mavenCentral() so that gradle builds fail

Author: maheshwarimrinal

android/build.gradle

@@ -4,6 +4,7 @@ def safeExtGet(prop, fallback) {
 
 buildscript {
     repositories {
+        mavenCentral()
         jcenter()
     }