Try fixing a bug encountered when using weasyprint in Pyinstaller context

[bartbroere]

When packaging weasyprint as a dependency in a Pyinstaller project, it looks for the VERSION file in the root sys._MEIPASS when the actual file ends up in sys._MEIPASS's subdirectory weasyprint. This pull request fixes that.

Maybe there's a reason the code is currently implemented this way. In that case I wouldn't mind to look for a solution to support all use cases.

Sample stack trace of the problem on runtime of an executable created with PyInstaller:

Traceback (most recent call last):
  File "site-packages\(...)\__init__.py", line 8, in <module>
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "c:\Python36\lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 627, in exec_module
  File "site-packages\weasyprint\__init__.py", line 41, in <module>
  File "pathlib.py", line 1174, in read_text
  File "pathlib.py", line 1161, in open
  File "pathlib.py", line 1015, in _opener
  File "pathlib.py", line 387, in wrapped
PermissionError: [Errno 13] Permission denied: 'C:\\Users\\bart\\AppData\\Local\\Temp\\_MEI826202\\VERSION'

[liZe]

Thank you!

Maybe there's a reason the code is currently implemented this way. In that case I wouldn't mind to look for a solution to support all use cases.

git blame gives the commit where the feature had been added, so… If it works for you, I suppose that it works everywhere 😄.