Update supported Python versions list

Per https://python-release-cycle.glitch.me/, Python 3.5 - 3.8 (and soon
to be 3.9) are the only currently supported Python versions. This change
updates the tox and travis configs, setup.py classifiers, and the
contributing guide to reflect those versions. Most notably, Python 2.7
reached end of life in April of this year and will no longer see any new
releases.

.travis.yml

@@ -4,21 +4,21 @@ language: python
 
 matrix:
   include:
+    - python: 3.8
+      env: TOX_ENV=py38
+    - python: 3.7
+      env: TOX_ENV=py37
     - python: 3.6
       env: TOX_ENV=py36
     - python: 3.5
       env: TOX_ENV=py35
-    - python: 3.4
-      env: TOX_ENV=py34
-    - python: 2.7
-      env: TOX_ENV=py27
     - python: pypy
       env: TOX_ENV=pypy
-    - python: 3.6
+    - python: 3.8
       env: TOX_ENV=flake8
 
 # Use tox to run tests on Travis-CI to keep one unified method of running tests in any environment
-install: 
+install:
   - pip install coverage coveralls tox
 
 # Command to run tests, e.g. python setup.py test

CONTRIBUTING.rst

@@ -99,7 +99,7 @@ Before you submit a pull request, check that it meets these guidelines:
 2. If the pull request adds functionality, the docs should be updated. Put
    your new functionality into a function with a docstring, and add the
    feature to the list in README.rst.
-3. The pull request should work for Python 2.7, 3.4, 3.5, 3.6, and PyPy. Check
+3. The pull request should work for Python 3.5, 3.6, 3.7, 3.8 and PyPy. Check
    https://travis-ci.org/bndr/pipreqs/pull_requests and make sure that the
    tests pass for all supported Python versions.
 

setup.py

@@ -44,12 +44,11 @@ setup(
         'Intended Audience :: Developers',
         'License :: OSI Approved :: Apache Software License',
         'Natural Language :: English',
-        'Programming Language :: Python :: 2',
-        'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
     ],
     test_suite='tests',
     entry_points={

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27, py34, py35, py36, pypy, flake8
+envlist = py35, py36, py37, py38, pypy, flake8
 
 [testenv]
 setenv =
@@ -9,7 +9,7 @@ deps =
     -r{toxinidir}/requirements.txt
 
 [testenv:flake8]
-basepython = python3.6
+basepython = python3.8
 commands = flake8 pipreqs
 deps =
     -r{toxinidir}/requirements.txt