Add py38 setup.py and tests

.travis.yml

@@ -8,6 +8,8 @@ matrix:
       env: TOX_POSARGS="-e py36"
     - python: "3.7"
       env: TOX_POSARGS="-e py37"
+    - python: "3.8"
+      env: TOX_POSARGS="-e py38"
 install:
   - travis_retry pip install tox
 script:

setup.py

@@ -30,7 +30,7 @@ setup(
     ],
     keywords='ethereum',
     # web3.py doesn't work on 3.5.2 and less (https://github.com/ethereum/web3.py/issues/1012)
-    python_requires='>=3.5.3,<3.8.0',
+    python_requires='>=3.5.3,<4',
     install_requires=[
         'web3==4.7.2',
         'eth-utils==1.8.4',

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist=
-    py{35,36,37}
+    py{35,36,37,38}
 
 [testenv]
 usedevelop=True
@@ -14,3 +14,4 @@ basepython=
     py35: python3.5
     py36: python3.6
     py37: python3.7
+    py38: python3.8