CoreFoundation memory management in RCTImageStoreManager

Summary:
I recently learned that CoreFoundation object lifecycle is not managed automatically by ARC.

RN appears to be leaking a few refs, this small stack of diffs cleans them up.

Changelog: [Internal][Fixed] Fixed memory management of CF objects in RCTImageStoreManager

Reviewed By: fkgozali

Differential Revision: D18308313

fbshipit-source-id: 35c1152753578825871c28e1070599cd409b3a34

Author: Peter Argany

Libraries/Image/RCTImageStoreManager.mm

@@ -178,6 +178,7 @@ - (id)sendRequest:(NSURLRequest *)request withDelegate:(id<RCTURLRequestDelegate
                                                         MIMEType:MIMEType
                                            expectedContentLength:imageData.length
                                                 textEncodingName:nil];
+    CFRelease(UTI);
 
     [delegate URLRequest:cancellationBlock didReceiveResponse:response];
     [delegate URLRequest:cancellationBlock didReceiveData:imageData];