clean(travis): remove shellcheck from before_install

Author: umarcor

.travis.yml

@@ -18,11 +18,8 @@ matrix:
       go: 1.12.x
       script: diff -u <(echo -n) <(gofmt -d -s .)
 
-before_install:
-  - mkdir -p bin
-  - curl -Lso bin/shellcheck https://github.com/caarlos0/shellcheck-docker/releases/download/v0.6.0/shellcheck
-  - chmod +x bin/shellcheck
-  - go get -u github.com/kyoh86/richgo
+before_install: go get -u github.com/kyoh86/richgo
+
 script:
   - PATH=$PATH:$PWD/bin richgo test -v ./...
   - go build