Docs: Update deploy token example to use https

I have enjoyed using deploy tokens in my projects. The example given on the docs page uses http://, and while it may be obvious to most that the particular URL protocol is irrelevant, I misunderstood this and assumed the deploy tokens only worked via http. This MR adds a single character to the example (changes http:// to https://) so that anyone else that makes a similar assumption in the future will at least be "secure by default". 😄

Thank you for the great product and great documentation!