TensorBoardLogger doesn't close SummaryWriter on finalize
🐛 Bug
The file handle managed by the SummaryWriter under the attribute _experiment in the TensorBoardLogger is never closed by any cleanup routines. This leaves a dangling file handle that restricts access to the output tfevent files until the parent script exists or the Jupyter kernel is restarted.
Please reproduce using the BoringModel
https://colab.research.google.com/drive/1QW9KWh7OjePfLuTPx51LhAONoHzFehvF?usp=sharing
To Reproduce
Use the above colab.

Expected behavior
TensorBoardLogger leaves no open file handles once it is finalized.
Environment

CUDA:

GPU:

Tesla T4


available:         True
version:           10.1


Packages:

numpy:             1.19.5
pyTorch_debug:     True
pyTorch_version:   1.7.0+cu101
pytorch-lightning: 1.1.6
tqdm:              4.41.1


System:

OS:                Linux
architecture:

64bit


processor:         x86_64
python:            3.6.9
version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020



Additional context