Update file(s) from wp-cli/.github

Do not crash when a broken symlink is encountered (#91)

"Broken symlink at {$relative_filepath}. Target missing at {$item->getLinkTarget()}."

Fix failing tests (#88)

Travis CI support in `wp scaffold plugin` was removed in wp-cli/scaffold-command#325, so all these `.travis.yml` files no longer exist.

Update file(s) from wp-cli/.github

Merge pull request #31 from wp-cli/30-create-directory-if-not-exists

Add `--create-target-dir` flag

Merge pull request #11 from runcommand/update-contributing

Update contributing section for README.md