fix session urls for the training feed
fix session urls for the training feed

In the JSON, the url is in "session", not "training", hence the
"undefined" result.

Fixes #260.

andy1138/scala-lang,jeantil/scala-lang,vl4ds/scala-lang,vl4ds/scala-lang,boldradius/scala-lang,andy1138/scala-lang,vl4ds/scala-lang,vl4ds/scala-lang,boldradius/scala-lang,jeantil/scala-lang,jeantil/scala-lang,boldradius/scala-lang,andy1138/scala-lang,jeantil/scala-lang,andy1138/scala-lang,boldradius/scala-lang