fix(CHANGELOG): use SSL for github URLs, recreate change entries

In trying to recreate recent CHANGELOG entries after the `deisctl` merge, I noticed we generated insecure URLs to point to GitHub issues. These work but always cause an unecessary redirect, so I fixed the `generate-changelog.sh` to use https:// and regenerated entries for previous releases back to when we first began using the script. I also removed an extraneous trailing space from the "v0.11.0 -> v0.12.0" headers.

`deisctl` CHANGELOG.md entries will appear in the next release:
```console
$ ./contrib/util/generate-changelog.sh v0.12.0 
### v0.12.0 -> HEAD

#### Features

 - [`a9c98c1`](https://github.com/deis/deis/commit/a9c98c1b06a4976fdb84c90b265b0afefc919c45) cmd: refresh-units accepts -t for tag, branch, or SHA
 - [`3158d8b`](https://github.com/deis/deis/commit/3158d8bbc99f5995c052547a120993158c2be80d) userdata: add deisctl to the coreos install
 - [`ee5f8a3`](https://github.com/deis/deis/commit/ee5f8a3e8a5af58650971df1c2845eee3a800752) contrib/digitalocean: Use native CoreOS integration
 - [`938f4eb`](https://github.com/deis/deis/commit/938f4eb3c2c490d0f92dce25d1fd4f684012dfee) cmd: add informative messages to install
 - [`c45fade`](https://github.com/deis/deis/commit/c45fadeebe09026599d90193ffd594016cd7e7e7) deisctl: colorize deisctl
 - [`615a2cb`](https://github.com/deis/deis/commit/615a2cb40aa7585428f596114b4270027e1e8ab5) start/stop: allow starting or stopping > 1 unit at a time
...
```

Closes #1934.

[skip ci]