Make UserAgent singleton for the example app

Author: hichamboushaba

example/src/main/java/org/wordpress/android/fluxc/example/di/AppConfigModule.java

@@ -15,6 +15,8 @@
 
 import java.lang.reflect.Field;
 
+import javax.inject.Singleton;
+
 import dagger.Module;
 import dagger.Provides;
 
@@ -41,6 +43,7 @@ public AppSecrets provideAppSecrets() {
     }
 
     @Provides
+    @Singleton
     public UserAgent provideUserAgent(Context appContext) {
         return new UserAgent(appContext, "fluxc-example-android");
     }