Fixed typo in header file documentation comment.

include/SDL_joystick.h

@@ -87,7 +87,7 @@ extern DECLSPEC const char *SDLCALL SDL_JoystickNameForIndex(int device_index);
 
 /**
  *  Open a joystick for use.
- *  The index passed as an argument refers tothe N'th joystick on the system.
+ *  The index passed as an argument refers to the N'th joystick on the system.
  *  This index is the value which will identify this joystick in future joystick
  *  events.
  *