fix Python 3.7 compatibility

[adamyi]

Python 3.7 removes re._pattern_type.

See python/cpython#1646

Otherwise,

Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Users/adamyi/notes_to_keep/notes_to_keep/notes_to_keep.py", line 57, in <module>
    main()
  File "/Users/adamyi/notes_to_keep/notes_to_keep/notes_to_keep.py", line 53, in main
    start(args)
  File "/Users/adamyi/notes_to_keep/notes_to_keep/notes_to_keep.py", line 49, in start
    gkeep.start(gaia, password, notes, num, pfx, no_time, no_label)
  File "/Users/adamyi/notes_to_keep/notes_to_keep/gkeep.py", line 66, in start
    label = createLabel(keep)
  File "/Users/adamyi/notes_to_keep/notes_to_keep/gkeep.py", line 49, in createLabel
    label = keep.createLabel(name)
  File "/usr/local/lib/python3.7/site-packages/gkeepapi/__init__.py", line 664, in createLabel
    if self.findLabel(name):
  File "/usr/local/lib/python3.7/site-packages/gkeepapi/__init__.py", line 686, in findLabel
    (isinstance(query, re._pattern_type) and query.search(label.name)): # pylint: disable=protected-access
AttributeError: module 're' has no attribute '_pattern_type'

[kiwiz]

Neat, thanks!