update python package requirements

requirements.txt

@@ -1,4 +1,5 @@
-Sphinx==3.2.1
-sphinx-rtd-theme==0.5.0
+Sphinx==3.5.4
+sphinx-rtd-theme==0.5.2
 sphinx-autobuild==0.7.1
-transifex-client==0.13.11
+transifex-client==0.14.2
+sphinx-intl==2.0.1