Fix typo in icon file name (flutter#6705)

At least, I think this fixes it. There was only one occurrence of
"frefresh_items" in the project. The icon file name does not begin with
'f'.

Fixes flutter#6693

(Yes, I know I need to clean up my local repo. Didn't want to
accidentally destroy it before I got the release out.)

flutter-idea/src/icons/FlutterIcons.java

@@ -21,7 +21,7 @@ private static Icon load(String path) {
 
   public static final Icon Phone = load("/icons/phone.png");
   public static final Icon Feedback = load("/icons/feedback.png");
-  public static final Icon RefreshItems = load("/icons/frefresh_items.png");
+  public static final Icon RefreshItems = load("/icons/refresh_items.png");
 
   public static final Icon Dart_16 = load("/icons/dart_16.svg");