Remove Ubuntu 14.04 for TensorFlow (#308)
Remove Ubuntu 14.04 for TensorFlow (#308)

From https://www.tensorflow.org/install/install_linux
> Ubuntu 16.04 or higher
TensorFlow doesn't officially support building on Ubuntu 14.04, no need to test on Bazel CI
bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration