Use new name for force_insert parameter introduced in pyelasticsearch 0.6.
Merge pull request #162 from jezdez/pyelasticsearch-0.6

Use new name for force_insert parameter introduced in pyelasticsearch 0.6.
Add Jannis to CONTRIBUTORS list
Remove second Jannis. :P

Jannis was already on there. I should read better next time.
Merge branch 'master' of https://github.com/mozilla/elasticutils