update en-GB translation
update en-GB translation

Change-Id: Ie33a152def419325281e7acdd7b4f6fff3fa7e0d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/268339
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

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