Update WP-CLI to v0.20.2
Update WP-CLI to v0.20.2

Release notes: http://wp-cli.org/blog/version-0.20.2.html

Closes #2463.

Signed-off-by: Andy Blyler <e3579b1e47f273529f0f929453e939a68ede9fd1@blyler.cc>

ablyler/homebrew-php,mkalkbrenner/homebrew-php,TomK/homebrew-php,dguyon/homebrew-php,philcook/homebrew-php