Consistently capitalize CLI options

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Made CLI option capitalization consistent in api/client.go

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Merge pull request #4461 from jamtur01/capital

Consistently capitalize CLI options