Merge pull request #29 from vonovak/patch-2

photo / photos consts

android/src/main/java/com/joshblour/reactnativepermissions/ReactNativePermissionsModule.java

     MICROPHONE,
     CONTACTS,
     EVENT,
-    PHOTOS;
+    PHOTO;
   }
 
   public ReactNativePermissionsModule(ReactApplicationContext reactContext) {
         return Manifest.permission.READ_CONTACTS;
       case EVENT:
         return Manifest.permission.READ_CALENDAR;
-      case PHOTOS:
+      case PHOTO:
         return Manifest.permission.READ_EXTERNAL_STORAGE;
       default:
         return null;
     }
   }
 
-}
+}