Fix Māori flag name (#1133)

## Description:

Removed unicode in Māori flag file name to prevent error, which lead to
not be able to start a game with it.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

tryout33

src/client/data/countries.json

@@ -1238,7 +1238,7 @@
     "name": "Malta"
   },
   {
-    "code": "Māori flag",
+    "code": "Maori flag",
     "continent": "Oceania",
     "name": "Māori Flag"
   },