fixed docs import error

docs/conf.py

@@ -15,6 +15,7 @@
 import sys
 import os
 from recommonmark.parser import CommonMarkParser
+from unittest.mock import MagicMock
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -334,5 +335,15 @@
                 None),
             }
 
-# Customize
+##### Customize ######
+
 autodoc_member_order = 'bysource'
+
+# Adresses import errors. Refer to:
+# https://docs.readthedocs.io/en/latest/faq.html#i-get-import-errors-on-libraries-that-depend-on-c-modules
+class Mock(MagicMock):
+    @classmethod
+    def __getattr__(cls, name):
+        return MagicMock()
+MOCK_MODULES = ['gym']
+sys.modules.update((mod_name, Mock()) for mod_name in MOCK_MODULES)