add Python 3.6 to travis matrix

.travis.yml

@@ -4,11 +4,7 @@ python:
   - "2.7"
   - "3.4"
   - "3.5"
-
-addons:
-  apt:
-    packages:
-      - libproj-dev   # otherwise gdal raises an error
+  - "3.6"
 
 before_install:
   - "wget http://repo.continuum.io/miniconda/Miniconda-latest-Linux-x86_64.sh -O miniconda.sh"
@@ -19,8 +15,9 @@ before_install:
   - "conda info -a"
 
 install:
-  - "conda create --yes -n test-env python=$TRAVIS_PYTHON_VERSION pip>=8.1 numpy>=1.10 cython>=0.25 pyproj>=1.9 gdal>=2.1 libgdal>=2.1 coverage>=4.2 shapely>=1.5"
+  - "conda create --yes -n test-env python=$TRAVIS_PYTHON_VERSION pip>=8.1 numpy>=1.10 cython>=0.25 pyproj>=1.9 gdal>=2.1 libgdal>=2.1"
   - "source activate test-env"
+  - "conda install --yes -c conda-forge shapely>=1.5 coverage>=4.3"
   - "pip install -r requirements.txt"
   - "pip install coveralls"
   - "pip install . --no-deps"