fix import

Author: hermanliang

Parse/Internal/LocalDataStore/OfflineStore/PFOfflineStore.m

@@ -28,6 +28,7 @@
 #import "PFUser.h"
 #import "PFWeakValue.h"
 #import "Parse_Private.h"
+#import "PFInstallation.h"
 
 typedef BFTask * (^PFOfflineStoreDatabaseExecutionBlock)(PFSQLiteDatabase *database);