Securing many http links to https links

Fix http link to https link for security, modify many link
http to https in the project.

Signed-off-by: Nguyen Hai Truong <truongnh@vn.fujitsu.com>

ADOPTERS.md

@@ -4,7 +4,7 @@ This is an alphabetical list of known adopters of Vitess. Some have already gone
 * [BetterCloud](https://bettercloud.com)
 * [CloudSigma](https://www.cloudsigma.com/)
 * [FlipKart](https://flipkart.com)
-* [GitHub](http://github.com/)
+* [GitHub](https://github.com/)
 * [HubSpot](https://product.hubspot.com/)
 * [JD](https://jd.com/)
 * [New Relic](https://newrelic.com)