Too restrictive version bounds for aeson, skylighting, happstack server, pandoc, pandoc-types and hoauth2

[sternenseemann]

gitit builds with:

• happstack-server 7.7.0
• aeson 1.5.4.1
• skylighting 0.10.2
• hoauth 1.16.0
• pandoc 2.11.3
• pandoc-types 1.22

but the version bounds in .cabal don't match that and should be adjusted.