Remove and mock doc dependencies because readthedocs is OOM

docs_requirements.txt

@@ -2,12 +2,9 @@ click
 fairseq
 future
 hypothesis<4.0
-joblib
+mock
 numpy
 onnx
-pandas
 pytorch-pretrained-bert
 requests
-scipy
 torchtext
-tensorboardX

pytext/docs/source/conf.py

@@ -17,6 +17,7 @@
 import os
 import sys
 
+import mock
 from sphinx.domains.python import PythonDomain
 
 
@@ -112,6 +113,15 @@
 #
 # html_sidebars = {}
 
+# Got this property from the official docs but doesn't seem to work
+# even in the latest version of Sphinx. Keeping for future compat.
+# autodoc_mock_imports = ['scipy', 'tensorboardX']
+
+# Manually mocking out the libraries to prevent requiring these modules
+MOCK_MODULES = ["scipy", "scipy.special", "tensorboardX"]
+for mod_name in MOCK_MODULES:
+    sys.modules[mod_name] = mock.Mock()
+
 
 # -- Options for HTMLHelp output ---------------------------------------------