feat: Google play services versioning (#333)

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### next
 
+* Add Gradle build config that allows a consumer to set Play Services Version from a root-project ext variable.
+
 ### 0.15.3
 
 * Fix crash on iOS: prevent insertion of nil values in the dictionary (https://github.com/rebeccahughes/react-native-device-info/pull/328)

README.md

@@ -81,6 +81,17 @@ Run your project (Cmd+R)
 <details>
     <summary>Android</summary>
 
+* **_optional_** in `android/build.gradle`:
+
+```gradle
+...
+  ext {
+    // dependency versions
+    googlePlayServicesVersion = "<Your Services Version>"
+  }
+...
+```
+
 * in `android/app/build.gradle`:
 
 ```diff

android/build.gradle

@@ -19,6 +19,8 @@ android {
 }
 
 dependencies {
+    def googlePlayServicesVersion = project.hasProperty('googlePlayServicesVersion') ? project.googlePlayServicesVersion : "+"
+
     compile 'com.facebook.react:react-native:+'
-    compile 'com.google.android.gms:play-services-gcm:+'
+    compile "com.google.android.gms:play-services-gcm:$googlePlayServicesVersion"
 }