Fix https blocking

Demos and docs are broken when pages are accessed via https.

Chrome: [blocked] The page at 'https://googlewebcomponents.github.io/' was loaded over HTTPS, but ran insecure content from 'http://googlewebcomponents.github.io/google-analytics/components/google-analytics/demo.html': this content should also be loaded over HTTPS.

Firefox: Blocked loading mixed active content "http://googlewebcomponents.github.io/google-calendar/components/google-calendar/demo.html"