build.gradle: Use new API for overriding version code.
build.gradle: Use new API for overriding version code.

ekager/focus-android,mozilla-mobile/focus-android,ekager/focus-android,jonalmeida/focus-android,jonalmeida/focus-android,ekager/focus-android,jonalmeida/focus-android,mozilla-mobile/focus-android,mozilla-mobile/focus-android,mozilla-mobile/focus-android,mozilla-mobile/focus-android,liuche/focus-android,jonalmeida/focus-android,liuche/focus-android,ekager/focus-android,liuche/focus-android,jonalmeida/focus-android,liuche/focus-android,liuche/focus-android,ekager/focus-android,mozilla-mobile/focus-android,ekager/focus-android,liuche/focus-android,jonalmeida/focus-android