Fix deprecation warning with assertEquals

While running framework_tensor_shape_test with bazel the following
warnings surface:
```
/home/ubuntu/.cache/bazel/_bazel_ubuntu/ad1e09741bb4109fbc70ef8216b59ee2/execroot/org_tensorflow/bazel-out/k8-opt/bin/tensorflow/python/framework_tensor_shape_test.runfiles/org_tensorflow/tensorflow/python/framework/tensor_shape_test.py:203: DeprecationWarning: Please use assertEqual instead.
  self.assertEquals(ctor, tensor_shape.Dimension)
```
This fix fixes the deprecation warnings.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>