Fixed misspelled parameter.

Fixes #287.

src/cocoa_window.m

@@ -127,7 +127,7 @@ static NSRect convertRectToBacking(_GLFWwindow* window, NSRect contentRect)
     _GLFWwindow* window;
 }
 
-- (id)initWithGlfwWindow:(_GLFWwindow *)initWndow;
+- (id)initWithGlfwWindow:(_GLFWwindow *)initWindow;
 
 @end