…-swandale

Link Issues and Pull Requests in the CHANGELOG

### What was the end-user problem that led to this PR?

When reviewing the CHANGELOG, it is difficult to navigate to the issue
or pull request that is relevant to the CHANGELOG item.

 ### What was your diagnosis of the problem?

The CHANGELOG should link to the referenced pull request/issue.

 ### What is your fix for the problem, implemented in this PR?

I added links to all of the issues referenced via BSD `sed`:

```
sed -i'' -Ee "s/#([0-9]+)/[#\1](https:\/\/github.com\/bundler\/bundler\/issues\/\1)/g" CHANGELOG.md
```