Bug fix: allow plugins and themes to be installed from zip file URLs that contain GET parameters

Without this bug fix, doing something like:

`wp plugin install http://downloads.wordpress.org/plugin/buddypress.1.7.2.zip?test`

would fail, because wp-cli wouldn't recognise that the URL contains a zip file. This is because the wp-cli code assumes that ".zip" must be the last 4 characters in the URL.

With this bug fix, the .zip file detection in URLs has been improved, so the above command works as expected.

This allows (for example), plugins/themes to be installed directly from private Amazon S3 URLs (which have GET parameters in the URLs). For example:

`wp plugin install 'http://s3.amazonaws.com/bucketname/plugin.zip?AWSAccessKeyId=123&Expires=456&Signature=abcdef'`

Note: for complex URLs that contain ampersands, it is usually necessary to enclose the URL in single quotes.