yojson 1.2.0 (provides support for some optional feature of atdgen 1.5.0)
Constraining yojson version for existing package atdgen-1.5.0.
I forgot to release yojson 1.2.0 when releasing atdgen 1.5.0.
Merge pull request #3292 from mjambon/master

yojson 1.2.0 + fix package atdgen 1.5.0