Update CHANGELOG.md

Merge pull request #213 from nf-core/dev

`dev` -> `master` for release `1.6.1`

Merge pull request #198 from nf-core/dev

Dev > Master for 1.6 release

Merge pull request #133 from nf-core/dev

Dev > Master, v1.5 release

Merge pull request #108 from nf-core/dev

v1.4 release Dev > Master

Merge pull request #70 from nf-core/dev

Dev > Master for 1.3 release

Merge pull request #60 from nf-core/dev

Version 1.2 release

Merge pull request #35 from nf-core/dev

Dev > Master for v1.1 release

Merge pull request #17 from nf-core/dev

Dev > Merge release 1.0 docker fix.