smallfix for unknown option '--skip-rebase' #85

[cikaldev]

cleancss -O2 --skip-rebase -o /path/to/file/style.css
error: unknown option '--skip-rebase'

reference issue: #85 thank you to: @input-username-here for suggest

• Update node clean-css using exact version [email protected]
• Fix typo on README (part example and license)

Note: This is just for temporary solution, before you make an update to functionality of this package. Please update the Readme section, so other people like me can use your package properly, specially for minify css code.

Regard's ian