Ignore vendor directories when running `phpcs`
Ignore vendor directories when running `phpcs`

It's not necessary to scan these files, and adds a huge amount of
unnecessary output to test runs.

aaemnnosttv/wp-cli,GaryJones/wp-cli,2ndkauboy/wp-cli,miya0001/wp-cli,GaryJones/wp-cli,trepmal/wp-cli,rodrigoprimo/wp-cli,miya0001/wp-cli,2ndkauboy/wp-cli,gitlost/wp-cli,rodrigoprimo/wp-cli,aaemnnosttv/wp-cli,trepmal/wp-cli,2ndkauboy/wp-cli,rodrigoprimo/wp-cli,gitlost/wp-cli,GaryJones/wp-cli,miya0001/wp-cli,aaemnnosttv/wp-cli,trepmal/wp-cli,gitlost/wp-cli