Upgrade omgeo to fix location search

Location search was broken because of azavea/python-omgeo#67.
By upgrading to the latest version of omgeo that includes azavea/python-omgeo#68,
this issue is fixed.

PyPI release of omgeo is blocked for now azavea/python-omgeo#70,
so we use the tag directly from GitHub instead.

src/mmw/requirements/base.txt

@@ -6,7 +6,7 @@ djangorestframework==3.13.1
 django-filter==21.1
 django-registration-redux==2.9
 django-extensions==3.1.5
-python-omgeo==6.1.0
+-e git+https://github.com/azavea/python-omgeo.git@6.2.0#egg=python-omgeo
 rauth==0.7.3
 djangorestframework-gis==0.17.0
 drf_yasg==1.20.0