Pin Cartopy to 0.17.* until we sort out problems (#270)

For some reason, the coast lines features are plotting on the entire
figure instead of only the land or ocean. Might be an error on our side.
For now, pin cartopy on CI to fix our docs.

Author: leouieda

environment.yml

@@ -18,7 +18,7 @@ dependencies:
     # Development requirements
     - pyproj
     - matplotlib
-    - cartopy
+    - cartopy==0.17.*
     - pytest
     - pytest-cov
     - pytest-mpl

requirements-dev.txt

@@ -1,7 +1,7 @@
 # Development requirements
 pyproj
 matplotlib
-cartopy
+cartopy=0.17.*
 pytest
 pytest-cov
 pytest-mpl