feat(l10n): add en-GB as a supported locale.
feat(l10n): add en-GB as a supported locale.

dannycoates/picl-idp,shane-tomlinson/fxa-auth-server,eoger/fxa-auth-server,shane-tomlinson/fxa-auth-server,shane-tomlinson/fxa-auth-server,dannycoates/picl-idp,mozilla/fxa-auth-server,TDA/fxa-auth-server,mozilla/fxa-auth-server,eoger/fxa-auth-server,mozilla/fxa-auth-server,TDA/fxa-auth-server,eoger/fxa-auth-server,dannycoates/picl-idp,shane-tomlinson/fxa-auth-server,TDA/fxa-auth-server,eoger/fxa-auth-server,TDA/fxa-auth-server,dannycoates/picl-idp,mozilla/fxa-auth-server