[emojier] Load locale file correctly

Summary:
ibus installs with the file en_GB.dict same with an underscore as a
separator for all regional variants.

The bcp47 name uses a hyphen.

Test Plan: I see emoticons

Reviewers: Plasma

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D25156