Godeps: Include github.com/xeipuuv/gojsonschema

Generated with:

  $ godep save ./...
  $ git mv Godeps/_workspace/src/github.com/xeipuuv/ vendor/github.com/

I'm not sure why I need the 'git mv ...'.  We've been keeping our
vendored content there since aab108d (update godeps and use by
makefile, 2017-03-24, #231), but my godep is still trying to save the
content under Godeps/_workspace.  Maybe it's because my system Go is
still 1.7.4?

Signed-off-by: W. Trevor King <wking@tremily.us>

Author: wking