Windowing System instructions.md typo (#1643)

Author: kroitor

exercises/concept/windowing-system/.docs/instructions.md

@@ -148,7 +148,7 @@ programWindow.position.y;
 
 ## 6. Change a program window
 
-Implement a `changeWindow` method that accepts a `ProgramWindow` instance as input and changes the window to the specified size and position.
+Implement a `changeWindow` function that accepts a `ProgramWindow` instance as input and changes the window to the specified size and position.
 The function should return the `ProgramWindow` instance that was passed in after the changes were applied.
 
 The window should get a width of 400, a height of 300 and be positioned at x = 100, y = 150.