build-unit-test-docker: use latest gitlint

gitlint release 0.18.0 contains the previously pointed to commit,
so pull it in directly rather than by reference now.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I741b0bbfe88f5361a4324bafdf7af883ad1a51c1
1 file changed