Merge pull request #314 from adundovi/master

Trying to fix make doc by forcing nbconvert==5.6.1 due to changes in …

.travis.yml

@@ -111,7 +111,7 @@ script:
     if [ $BUILD_DOC ]; then
       echo "Building Documentation"
       pip3 install wheel
-      pip3 install m2r==0.2.1 Sphinx==1.7.9 nbsphinx==0.3.5 breathe==4.10.0 exhale==0.2.3  sphinx-rtd-theme==0.4.3 recommonmark==0.6.0
+      pip3 install m2r==0.2.1 Sphinx==1.7.9 nbconvert==5.6.1 nbsphinx==0.3.5 breathe==4.10.0 exhale==0.2.3  sphinx-rtd-theme==0.4.3 recommonmark==0.6.0
       cmake ..
       make doc
       touch doc/.nojekyll