Enable shellcheck for contrib/ (#9122)

Today we have many contributions to contrib/offline/ and some PRs
contained invalid coding style for those scripts.
This enables shellcheck to make such invalid coding style easily.

.gitlab-ci/shellcheck.yml

@@ -11,6 +11,6 @@ shellcheck:
     - cp shellcheck-"${SHELLCHECK_VERSION}"/shellcheck /usr/bin/
     - shellcheck --version
   script:
-    # Run shellcheck for all *.sh except contrib/
-    - find . -name '*.sh' -not -path './contrib/*' -not -path './.git/*' | xargs shellcheck --severity error
+    # Run shellcheck for all *.sh
+    - find . -name '*.sh' -not -path './.git/*' | xargs shellcheck --severity error
   except: ['triggers', 'master']