build: add travis support for shellcheck

.travis.yml

@@ -0,0 +1,16 @@
+sudo: required
+
+language: bash
+
+services:
+  - docker
+
+before_install:
+  - docker pull koalaman/shellcheck
+
+script:
+  - docker run -v $(pwd):/scripts koalaman/shellcheck /scripts/ovh-api-bash-client.sh
+
+matrix:
+  fast_finish: true
+