Bugfix Release HTMLMerger

If one of the html reports wasn't created by a parallel job the merger will not longer throw an exception.
The Merger will show a warning that an expected html report wasn't found.

What's Changed

• Update CHANGELOG.md by @Arhell in #90
• Bugfix/91 fixing html merger by @vansari in #92

Full Changelog: 1.2.3...1.2.4