use main python versions

Author: akira-dev

.travis.yml

@@ -3,7 +3,7 @@ language: python
 python:
   - '3.5'
   - '3.6'
-  - '3.7'
+  - '3.8'
   - 'pypy3'
 script:
   - pip install .[dev]

setup.py

@@ -14,9 +14,9 @@
     classifiers=[
         'Framework :: Flask',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.8',
         'License :: OSI Approved :: MIT License',
     ],
     keywords='web api rest jsonapi flask sqlalchemy marshmallow',