Log Message:
khal: update to 0.9.7.

0.9.7
=====
released 2017-09-15

* FIX don't crash when editing events with datetime UNTIL properties
* FIX `search` will no longer break on overwritten events with a master event

* CHANGE `search` will now print one line for every different event in a
  recurrence set, that is one line for the master event, and one line for every
  different overwritten event