Merge pull request #1741 from Baichenghui/master

Word corrections

SDWebImage/SDWebImageManager.m

@@ -109,7 +109,7 @@
     // Invoking this method without a completedBlock is pointless
     NSAssert(completedBlock != nil, @"If you mean to prefetch the image, use -[SDWebImagePrefetcher prefetchURLs] instead");
 
-    // Very common mistake is to send the URL using NSString object instead of NSURL. For some strange reason, XCode won't
+    // Very common mistake is to send the URL using NSString object instead of NSURL. For some strange reason, Xcode won't
     // throw any warning for this type mismatch. Here we failsafe this error by allowing URLs to be passed as NSString.
     if ([url isKindOfClass:NSString.class]) {
         url = [NSURL URLWithString:(NSString *)url];