Update get-translator-credits script to run from project root

scripts/get-translator-credits.py

@@ -8,7 +8,7 @@ from babel import Locale
 authors_by_locale = defaultdict(set)
 
 file_listing = subprocess.Popen(
-    "find ../wagtail -iname *.po", shell=True, stdout=subprocess.PIPE
+    "find ./wagtail -iname *.po", shell=True, stdout=subprocess.PIPE
 )
 
 for file_listing_line in file_listing.stdout: