Forcing installation of cython to support netcdf4 1.2.8

cython is a compulsory dependency of netcdf4 starting from 1.2.8, but since it's
a build-time dependency conda doesn't install it, netdcf4 is compiled
externally. Lack of cython doesn't break netcdf4 library, but it does break
compliance checker, because it uses `pkg_resource` lib to check if dependencies
for plugins are installed and `pkg_resource` reports that cython is needed to
import `netcdf4` which isn't true.

.travis/environment_py27.yaml

@@ -10,7 +10,7 @@ dependencies:
 - numexpr
 - rasterio
 - singledispatch
-- netcdf4 <= 1.2.7 # char2string and compliance checker related problems in 1.2.8
+- netcdf4
 - psycopg2
 - gdal
 - dask
@@ -25,6 +25,7 @@ dependencies:
 - matplotlib # pixel drill app
 - pathlib
 - compliance-checker = 3.0.3
+- cython # used by netcdf4 at compile only, but needed for compliance checker to load plugins
 - pygeoif = 0.6 # compliance-checker 3.0.3 fails with 0.7
 - paramiko # for simple-replicas
 - sshtunnel # for simple-replicas

.travis/environment_py35.yaml

@@ -11,7 +11,7 @@ dependencies:
 - numexpr
 - rasterio
 - singledispatch
-- netcdf4 <= 1.2.7 # char2string and compliance checker related problems in 1.2.8
+- netcdf4
 - psycopg2
 - gdal
 - dask
@@ -26,6 +26,7 @@ dependencies:
 - matplotlib # pixel drill app
 - pathlib
 - compliance-checker = 3.0.3
+- cython # used by netcdf4 at compile only, but needed for compliance checker to load plugins
 - pygeoif = 0.6 # compliance-checker 3.0.3 fails with 0.7
 - paramiko # for simple-replicas
 - sshtunnel # for simple-replicas