travis: check commits for whitespace errors

https://github.com/opencontainers/runtime-spec/pull/366/files/af056a3e9e61c0dc4738f24c35816d2a02d86607#r59321215

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

Author: vbatts

.travis.yml

@@ -14,5 +14,5 @@ install: true
 script:
   - go vet -x ./...
   - make .golint
-  - $HOME/gopath/bin/git-validation -run DCO,short-subject -v -range ${TRAVIS_COMMIT_RANGE}
+  - $HOME/gopath/bin/git-validation -run DCO,short-subject,dangling-whitespace -v -range ${TRAVIS_COMMIT_RANGE}