Bump version to 3.0.8

Due to our (new) convention plugins inherit their versions from the
OpenProject core. The next stable release of the OpenProject core is
3.0.8.
fixed dep in gemspec
Update stable to v3.0.8
Adapt version to corresponding OpenProject core version
fixes textile parsing with "document" and other in text

Otherwise only the document will be parsed but no #, or other OP specific textile extensions
correctly uses gsub! (nil on return)
Update stable to v3.0.11
Added event type for documents class.
Adapt version to corresponding OpenProject core version.
Update stable to v3.0.12