Update required python packages for read-the-docs.

doc/requirements/dev.txt

 pyparsing==1.5.7
-Pygments==1.6
-Sphinx==1.2.2
-actdiag==0.5.3
-blockdiag==1.4.4
+Pygments==2.2.0
+Sphinx==1.6.3
+actdiag==0.5.4
+blockdiag==1.5.3
 sphinxcontrib-actdiag==0.7.2
-sphinxcontrib-doxylink==1.3
-sphinx_rtd_theme==0.1.6
-breathe==3.1.0
+sphinxcontrib-doxylink==1.3.0
+sphinx_rtd_theme==0.2.4
+breathe==4.6.0