Disable colored output in shellcheck

shellcheck defaults to using colors in its output.  Unfortunately,
jenkins is unable to process bash-style colors in the console log, so in
practice, when colors are used, the jenkins logs end up like:

[1mIn jenkins/userid-validation line 25:[0m
[0mif [ "x${COMMITTER_EMAIL}" == "x" ]; then[0m
[32m     ^-------------------^ SC2268 (style): Avoid x-prefix in comparisons as it no longer serves a purpose.[0m

[1mDid you mean: [0m
if [ "${COMMITTER_EMAIL}" == "" ]; then

With lots of control characters.  This is annoying to review in build
scripts, which are primarily being read from disk somewhere.

The above log was pulled from the review here:
https://jenkins.openbmc.org/job/CI-MISC/job/ci-openbmc-build-scripts/455/console

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ibc827039150f7018b31a63ac11fa7c19776414c9
diff --git a/scripts/format-code.sh b/scripts/format-code.sh
index 47cb0f7..152a5b2 100755
--- a/scripts/format-code.sh
+++ b/scripts/format-code.sh
@@ -70,7 +70,7 @@
 shell_scripts="$(git ls-files | xargs -n1 file -0 | \
                  grep -a "shell script" | cut -d '' -f 1)"
 for script in ${shell_scripts}; do
-  shellcheck -x "${script}" || ${shellcheck_allowfail}
+  shellcheck --color=never -x "${script}" || ${shellcheck_allowfail}
 done
 
 # Allow called scripts to know which clang format we are using