Fixed spelling mistake, fixes #7

src/game.js

@@ -15,7 +15,7 @@ class Game {
     }
 
     changeScreen(screen) {
-        if (this.mainSCreen !== undefined) {
+        if (this.mainScreen !== undefined) {
             this.mainScreen.removeListeners();
         }
 

src/screen.js

@@ -45,7 +45,7 @@ class Screen {
 
     removeListeners() {
         for (let listener of this.listeners) {
-            console.log(document.removeElementListener(listener.type, listener.callback));
+            document.removeEventListener(listener.type, listener.callback);
         }
     }