Merge pull request #1 from punker76/master

fix parameter and add zoom to extent for multiple layers (openstreetmap)
bring in zoom mapping property

I was getting a gray box when I added a map to a post, and from what
I found online this was because the zoom property wasn't being added to
the google maps options.

This fixes my issue and makes my maps work!
Merge pull request #3 from kitchen/zoom-fix

bring in zoom mapping property
Merge branch 'upstream/master'

Conflicts:
	_plugins/jekyll_mapping.rb