Support new sphinx version without warning. Needed for our CI.

doc/conf.py

@@ -42,10 +42,16 @@ todo_include_todos = True
 napoleon_google_docstring = False
 napoleon_include_special_with_doc = False
 
+# We do it like this to support multiple sphinx version without having warning.
+# Our buildbot consider warning as error.
 try:
+    from sphinx.ext import imgmath
+    extensions.append('sphinx.ext.imgmath')
+except ImportError:
+    try:
         from sphinx.ext import pngmath
         extensions.append('sphinx.ext.pngmath')
-except ImportError:
+    except ImportError:
         pass