added version of sphinxcontrib-images

requirements.txt

@@ -24,7 +24,7 @@ sphinx_design==0.5.0
 sphinxcontrib-applehelp==1.0.8
 sphinxcontrib-devhelp==1.0.6
 sphinxcontrib-htmlhelp==2.0.5
-sphinxcontrib-images
+sphinxcontrib-images==0.9.4
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.7
 sphinxcontrib-serializinghtml==1.1.10