Fix to the webp regex so that URLs such as '/images/foo.jpg' work when the src/url does not include 'http[s]?'

[picasticks]

This way any src URL, such as "/wp-content/uploads/..." or "//example.com/wp-content/uploads" or even "sftp://example.com/wp-content/uploads" will work with the WebP feature.

The problem on our sites was that these URLs were being skipped by the WebP feature.

This was a very simple fix to just remove the https[s]? from the regular expression.

Thanks for the plugin!