fix: replace rectangle with square in lesson 5 (#571)

fix issue #570

Author: dupoxy

course/lesson-5-your-first-function/lesson.tres

@@ -99,7 +99,7 @@ title = ""
 type = 0
 text = "Every time we call [code]move_and_rotate()[/code], the two functions [code]move_forward(200)[/code] and [code]turn_right(90)[/code] are called in sequence.
 
-In this simple example, it may not feel super useful. Here's a more useful and realistic one: a function to draw any rectangle.
+In this simple example, it may not feel super useful. Here's a more useful and realistic one: a function to draw any square.
 
 The following function uses [i]parameters[/i], which we will explore in the next lesson.