This fixes a potential FileNotFoundError when clearing the cache
manually, using the method from
https://github.com/davidhalter/jedi-vim/pull/625.
Traceback:
```
File "…/jedi/evaluate/imports.py", line 342, in _do_import
module = _load_module(self._evaluator, module_path, source, sys_path, parent_module)
File "…/jedi/evaluate/imports.py", line 457, in _load_module
cached = load_parser(path)
File "…/jedi/parser/utils.py", line 72, in load_parser
return ParserPickling.load_parser(path, p_time)
File "…/jedi/parser/utils.py", line 126, in load_parser
with open(self._get_hashed_path(path), 'rb') as f:
FileNotFoundError: [Errno 2] No such file or directory: '…/.cache/jedi/cpython-35/759d60e96c76f41ffd882d9b8d844899.pkl'
```