Dash in list of illegal chars

[dextep]

• Change in CHANGELOG.md described (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[Siedlerchr]

First update your fork by merging in upstream/master
Push to origin
Then create a new branch and do the fix
Then push the branch
Then all should be fine

[dextep]

Thanks @Siedlerchr! That was a bit confused for me, sorry for that. Hope right now is fine :)