Specify Sphinx version >=1.8,<2 in dev dependencies

Signed-off-by: Håkon Wiik Ånes <[email protected]>

Author: hakonanes

requirements-dev.txt

@@ -67,7 +67,7 @@ seaborn==0.9.0
 six==1.12.0
 snowballstemmer==1.2.1
 sphinx-rtd-theme==0.4.3
-sphinx==1.7.6
+sphinx>=1.8,<2
 sphinxcontrib-napoleon==0.7
 sphinxcontrib-websupport==1.1.0
 testpath==0.4.2