Wrong action type on queryFailure action creator

**Describe the bug:** probably just a typo: (`success` type on failure action creator)

https://github.com/netlify/netlify-cms/blob/f801b192211b1e1953ced969a3093eab9e04e14d/packages/netlify-cms-core/src/actions/search.js#L75-L77

although, the failure handler *is* missing from search reducer.
idk what is the expected response to a failed query.

**To Reproduce:** possible bug, but never happened to me.

**Expected behavior:** `¯\_(ツ)_/¯`

**Applicable Versions:** always there, since this feature was added in #186

**Additional context**

was just reading through code, while solving some of race-conditions I introduced in my [fork](https://github.com/campus-online/cms).