Fix failing Snapshotter spec

In 566b9fe69 we changed the behavior of Snapthotter to not raise an
error when it is unable to parse a line of the take-snapshot.js script
as JSON, but we failed to update the spec. This commit follows up with
this work.

Change-Id: I720050e47e0d4b35eac170d8b1857a7e8823ae55