Fix CHANGELOG.md template

MSP-11837

It appears that the contents of `CHANGELOG.md` and `app/templates/CHANGELOG.md.tt` got swapped.  The template had the changes from `metasploit-version` itself while `CHANGELOG.md` had just the starting template.  I think this occured because I copied `CHANGELOG.md` to `app/templates/CHANGELOG.md.tt` and then tried running `metasploit-version install` on top of the project itself.

# Verification Steps

## Specs
- [ ] `rake spec`
- [ ] VERIFY no failues

## Cucumber
- [ ] `rake cucumber`
- [ ] VERIFY no failures

## CHANGELOG.md template
- [ ] `open app/templates/CHANGELOG.md.tt`
- [ ] VERIFY `Changelog` header at top of file
- [ ] VERIFY releases a higher header number than `Changelog`
- [ ] VERIFY there are no actual changes references in the file.

## CHANGELOG.md
- [ ] `open CHANGELOG.md`
- [ ] VERIFY `Changelog` header at top of file
- [ ] VERIFY releases a higher header number than `Changelog`
- [ ] VERIFY #3 is in Next Release
- [ ] VERIFY #2 and #1 are in 

# Post-merge Steps

Perform these steps prior to pushing to master or the build will be broke on master.

## Version
- [ ] Edit `lib/metasploit/version/version.rb`
- [ ] Remove `PRERELEASE` and its comment as `PRERELEASE` is not defined on master.

## Gem build
- [ ] gem build *.gemspec
- [ ] VERIFY the gem has no '.pre' version suffix.

## RSpec
- [ ] `rake spec`
- [ ] VERIFY version examples pass without failures

## Commit & Push
- [ ] `git commit -a`
- [ ] `git push origin master`