message: Slice futher of bazel build target so that Travis CI could build cache.
diff: @@ -63,7 +63,7 @@ bazel build \
  --noshow_loading_progress \
  --verbose_failures \
  --test_output=errors \
  - -- //tensorflow_io/core:all
  + -- //tensorflow_io/core:python/ops/libtensorflow_io.so
  rm -rf build && mkdir -p build
  