Add shfmt check on Travis CI

.travis.yml

@@ -32,6 +32,14 @@ jobs:
           doctoc --title='## Table of Contents' --github README.md &&
           diff -q README.md README.md.tmp
 
+    - stage: Test
+      env:
+        - TEST: shfmt check
+      script:
+        - docker run -it --rm -v "$(pwd)":/sh -w /sh jamesmstone/shfmt -i 2 -l -w -ci .
+        - git diff --color
+        - git diff --stat=220 --color --exit-code
+
     - stage: Test
       env:
         - TEST: Shell Check