Update tensorflow 1.11 version recognition
Update tensorflow 1.11 version recognition

In tensorflow 1.11 tensorflow.default doesn't have the PLUGIN_LOADERS attribute, but the _PLUGINS one.
Moreover, the program.TensorBoard class constructor can take the default arguments correctly if they're not passed, this avoids the need to make another if branch for the 1.11 version.
lspvic/jupyter_tensorboard,lspvic/jupyter_tensorboard