Minor correction in API doc

include/SFML/System/Mutex.hpp

@@ -138,7 +138,7 @@ private :
 ///
 /// SFML mutexes are recursive, which means that you can lock
 /// a mutex multiple times in the same thread without creating
-/// a deadlock. In this case, the first call to Lock() behaves
+/// a deadlock. In this case, the first call to lock() behaves
 /// as usual, and the following ones have no effect.
 /// However, you must call unlock() exactly as many times as you
 /// called lock(). If you don't, the mutex won't be released.