update en-GB translation
update en-GB translation

Change-Id: Ide9ce4f0e8e07766e36bda70eccb13644307e980
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/292466
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

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