Pin cvxpy to 1.1.7 (#955)

1.1.8 is incompatible with our version of numpy.

http://b/179264579

Author: rosbo

Dockerfile

@@ -188,6 +188,8 @@ RUN pip install mpld3 && \
     pip install ImageHash && \
     pip install ecos && \
     pip install CVXcanon && \
+    # b/179264579 cvxpy 1.1.8 requires numpy >= 1.20
+    pip install cvxpy==1.1.7 && \
     pip install fancyimpute && \
     pip install pymc3 && \
     pip install imagecodecs && \