Replace http:// with https:// where applicable

The testcases will be updated automatically in a separate commit.

.github/CONTRIBUTING.md

@@ -6,7 +6,7 @@ Note that bug reports and feature requests for related projects should be filed
 
 ## i3 bug reports and feature requests
 
-1. Read the [debugging instructions](http://i3wm.org/docs/debugging.html).
+1. Read the [debugging instructions](https://i3wm.org/docs/debugging.html).
 2. Make sure you include a link to your logfile in your report (section 3).
 3. Make sure you include the i3 version number in your report (section 1).
 4. Please be aware that we cannot support compatibility issues with
@@ -25,11 +25,11 @@ Note that bug reports and feature requests for related projects should be filed
   ”feature request” or ”enhancement” in its title.
 * Use the `next` branch for developing and sending your pull request.
 * Use `clang-format` to format your code.
-* Run the [testsuite](http://i3wm.org/docs/testsuite.html)
+* Run the [testsuite](https://i3wm.org/docs/testsuite.html)
 
 ## Finding something to do
 
 * Find a [reproducible bug](https://github.com/i3/i3/issues?utf8=%E2%9C%93&q=is%3Aopen+label%3Areproducible+label%3Abug+) from the issue tracker. These issues have been reviewed and confirmed by a project contributor.
 * Find an [accepted enhancement](https://github.com/i3/i3/issues?utf8=%E2%9C%93&q=is%3Aopen+label%3Aaccepted+label%3Aenhancement) from the issue tracker. These have been approved and are ok to start working on.
 
-There's a very good [overview of the codebase](http://i3wm.org/docs/hacking-howto.html) available to get you started.
+There's a very good [overview of the codebase](https://i3wm.org/docs/hacking-howto.html) available to get you started.

.github/ISSUE_TEMPLATE.md

@@ -2,7 +2,7 @@ Output of `i3 --moreversion 2>&- || i3 --version`:
 
 _REPLACE: i3 version output_
 
-URL to a logfile as per http://i3wm.org/docs/debugging.html:
+URL to a logfile as per https://i3wm.org/docs/debugging.html:
 
 _REPLACE: URL to logfile_