Change Pontoon's {locale} to {android_locale}

This is because Pontoon locales don't match exactly with the CWS
locales, while android_locale has more matches.

Bug: twpowertools:40
Change-Id: I6b2a675f2391f3802b2582b100e328a0a30c71ae
diff --git a/i18n-config.toml b/i18n-config.toml
index 4cf7914..10a1b23 100644
--- a/i18n-config.toml
+++ b/i18n-config.toml
@@ -14,4 +14,4 @@
 
 [[paths]]
   reference = "src/static/_locales/en/messages.json"
-  l10n = "src/static/_locales/{locale}/messages.json"
+  l10n = "src/static/_locales/{android_locale}/messages.json"