Merge pull request #34 from skirpichev/py3.7

Enable py3.7 in Travis build matrix and fix broken import

.travis.yml

@@ -1,11 +1,12 @@
 language: python
 python:
   - 3.6
+  - 3.7-dev
 install:
   - pip install -r requirements.txt
   - pip install coveralls
   - python setup.py -V
 script:
   - make coverage
 after_success:
-  coveralls
+  coveralls

matchpy/expressions/expressions.py

@@ -51,7 +51,7 @@
 import keyword
 from enum import Enum, EnumMeta
 # pylint: disable=unused-import
-from typing import (Callable, Iterator, List, NamedTuple, Optional, Set, Tuple, TupleMeta, Type, Union)
+from typing import Callable, Iterator, List, NamedTuple, Optional, Set, Tuple, Type, Union
 # pylint: enable=unused-import
 
 from multiset import Multiset