Merge pull request #1437 from marquiz/devel/mdlint

scripts/test-infra: bump mdlint to v0.13.0

Author: k8s-ci-robot

scripts/test-infra/mdlint.sh

@@ -1,6 +1,6 @@
 #!/bin/bash -e
 
 # Install mdl
-gem install mdl -v 0.12.0
+gem install mdl -v 0.13.0
 # Run verify steps
 find docs/ -path docs/vendor -prune -false -o -name '*.md' | xargs mdl -s docs/mdl-style.rb