Fix theano test (#941)

http://b/178107003

Author: Philmod

Dockerfile

@@ -83,7 +83,8 @@ RUN apt-get install -y libfreetype6-dev && \
     pip install keras && \
     pip install keras-tuner && \
     pip install flake8 && \
-    pip install theano-pymc && \
+    # Pinned because it breaks theano test with the latest version (b/178107003).
+    pip install theano-pymc==1.0.11 && \
     pip install python-Levenshtein && \
     pip install hep_ml && \
     # NLTK Project datasets