cleanup: build-unit-test-docker.sh: use double brackets instead of single

[[ ... ]] reduces errors as no pathname expansion or word splitting
takes place between [[ and ]]. In addition, [[ ... ]] allows for
regular expression matching while [ ... ] does not.

Change-Id: Id68819d850fe9053f41cf7ef347f0e1a55b6d129
Signed-off-by: Patrick Venture <venture@google.com>
1 file changed