Check shell script format via shfmt on Travis CI

Author: PeterDaveHello

.travis.yml

@@ -37,6 +37,15 @@ jobs:
       - npm i -g echint
     script:
       - echint
+  - stage: Static tests
+    env:
+      - task=shfmt
+    services:
+      - docker
+    script:
+      - docker run -it --rm -v "$(pwd)":/sh -w /sh peterdavehello/shfmt:2.5.0 -sr -i 2 -l -w -ci .
+      - git diff --color
+      - git diff --stat=220 --color --exit-code
 
 # test all echo functions on difference shell on Linux
   - stage: Ubuntu runtime test