File prev_skip_content opened but not closed.

https://github.com/facebook/hhvm/blob/50c593d591302bf1490c974dcbe0e02e6a4fc5f3/hphp/test/tools/import_spec_test.py#L149
The file descriptor prev_skip_content in the file `hhvm/hphp/test/tools/import_spec_test.py` is opened but not closed. Besides, it would be better if we can use
```python
with open("file.txt", "r") as prev_skip_content:
```

instead. Can I raise a PR for this?