Incorrect results with --exclude-tags-regex

[christopher-dG]

As a workaround for #724, I hacked a regex for --exclude-tags-regex to accept any string except my specific tag: ^(?!v0\.6\.0$). This works in that the only section generated is for tag v0.6.0, but the "Merged pull requests" sections contains far more PRs than were actually merged in that time frame (30/33 total PRs are displayed, the correct number is 9).

Tested with this command:

# Gives correct results, but contains sections for all tags
github_changelog_generator -t <token> -u invenia -p PkgTemplates.jl

# Gives incorrect results for v0.6.0 section (the only section)
github_changelog_generator -t <token> -u invenia -p PkgTemplates.jl --exclude-tags-regex '^(?!v0\.6\.0$)'