update en-GB translation
update en-GB translation

Change-Id: I2d380326b76e846a34c5339605d78e2f25cfb7c6
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/226746
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms