Normalize generated changelog to remove redundant information and whitespace

[weierophinney]

Feature Request

Q	A
New Feature	enhancement
RFC	no
BC Break	no

Summary

Currently, the jwage/changelog-generator -generated content includes:

-----

### Release Notes for [1.0.0](https://github.com/mezzio/mezzio-cors/milestone/1)



### 1.0.0

Note:

• the extra line breaks
• the repeated "1.0.0" references

The suggestion is to normalize this to:

• never have more than one empty line at a time
• remove the extraneous version references