Fix Content-Type header checking of React/RCTJavascriptLoader.mm face…

…book#15791

Summary:
To fix this issue: facebook#15791
Closes facebook#15792

Differential Revision: D5813101

Pulled By: shergin

fbshipit-source-id: fd3eb6f1d9ccdeb5373d1ba2b2df173ff7a8e986

React/Base/RCTJavaScriptLoader.mm

@@ -284,16 +284,17 @@ static void attemptAsynchronousLoadOfBundleAtURL(NSURL *scriptURL, RCTSourceLoad
 
     // Validate that the packager actually returned javascript.
     NSString *contentType = headers[@"Content-Type"];
-    if (![contentType isEqualToString:@"application/javascript"] &&
-        ![contentType isEqualToString:@"text/javascript"]) {
-      NSString *description = [NSString stringWithFormat:@"Expected Content-Type to be 'application/javascript' or 'text/javascript', but got '%@'.", contentType];
+    NSString *mimeType = [[contentType componentsSeparatedByString:@";"] firstObject];
+    if (![mimeType isEqualToString:@"application/javascript"] &&
+        ![mimeType isEqualToString:@"text/javascript"]) {
+      NSString *description = [NSString stringWithFormat:@"Expected MIME-Type to be 'application/javascript' or 'text/javascript', but got '%@'.", mimeType];
       error = [NSError errorWithDomain:@"JSServer"
                                   code:NSURLErrorCannotParseResponse
                               userInfo:@{
                                          NSLocalizedDescriptionKey: description,
                                          @"headers": headers,
                                          @"data": data
-                                         }];
+                                       }];
       onComplete(error, nil);
       return;
     }