fix(android): bump minSdkVersion from 16 to 21

Author: willflemmer

android/build.gradle

@@ -29,7 +29,7 @@ android {
   compileSdkVersion getExtOrIntegerDefault('compileSdkVersion')
   buildToolsVersion getExtOrDefault('buildToolsVersion')
   defaultConfig {
-    minSdkVersion 16
+    minSdkVersion 21
     targetSdkVersion getExtOrIntegerDefault('targetSdkVersion')
     versionCode 1
     versionName "1.0"