Update sphinx_rtd_theme from 0.4.3 to 0.5.0

requirements.txt

@@ -1,7 +1,7 @@
 mock==3.0.5
 python-igraph==0.8.2
 netdispatch==0.0.5
-sphinx_rtd_theme==0.4.3
+sphinx_rtd_theme==0.5.0
 numpy==1.17.*
 future==0.17.*
 networkx==2.3