Small fix request for legacy release

[koenvanderdrift]

Please update the following two lines in the legacy release to make the compiler happy:

In MDProgressHUD.h:

-typedef void (^MBProgressHUDCompletionBlock)();
+typedef void (^MBProgressHUDCompletionBlock)(void);

In MDProgressHUD.m:

-- (void)showAnimated:(BOOL)animated whileExecutingBlock:(dispatch_block_t)block completionBlock:(void (^)())completion {
+- (void)showAnimated:(BOOL)animated whileExecutingBlock:(dispatch_block_t)block completionBlock:(void (^)(void))completion {

I tried to push these, but I do not have the privileges.