Add setWithPriority support to ref.

Author: FrankSalad

ios/Firestack/FirestackDatabase.m

@@ -400,6 +400,17 @@ - (id) init
     }];
 }
 
+RCT_EXPORT_METHOD(setWithPriority:(NSString *) path
+                  data:(NSDictionary *)data
+                  priority: (NSDictionary *)priority
+                  callback:(RCTResponseSenderBlock) callback)
+{
+    FIRDatabaseReference *ref = [self getPathRef:path];
+    [ref setValue:[data valueForKey:@"value"] andPriority:[priority valueForKey:@"value"] withCompletionBlock:^(NSError * _Nullable error, FIRDatabaseReference * _Nonnull ref) {
+        [self handleCallback:@"setWithPriority" callback:callback databaseError:error];
+    }];
+}
+
 RCT_EXPORT_METHOD(update:(NSString *) path
                   value:(NSDictionary *)value
                   callback:(RCTResponseSenderBlock) callback)

lib/modules/database/reference.js

@@ -50,6 +50,18 @@ export default class Reference extends ReferenceBase {
     return promisify('set', FirestackDatabase)(path, _value);
   }
 
+  /**
+   *
+   * @param value
+   * @returns {*}
+   */
+  setWithPriority(value: any, priority: any) {
+    const path = this._dbPath();
+    const _value = this._serializeAnyType(value);
+    const _priority = this._serializeAnyType(priority);
+    return promisify('setWithPriority', FirestackDatabase)(path, _value, _priority);
+  }
+
   /**
    *
    * @param val