Use `wp_parse_args()` where we can
Merge branch 'master' of git://github.com/wp-cli/wp-cli
Merge branch 'master' of git://github.com/wp-cli/wp-cli
Let's use the simpler `array_merge()` instead of `wp_parse_args()`
Merge pull request #643 from johnbillion/master

Use `wp_parse_args()` where we can