update en-GB translation
update en-GB translation

Change-Id: I232360229b25ca34b49511d40a5236fa087f7226
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/213720
Tested-by: Jenkins

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