Battling coverage measurements on Python 2 and PyPy

Turns out the concurrent.futures backport actually provides a package
'concurrent', so my fallback was never executed.

Makefile

@@ -15,6 +15,6 @@ coverage:
 
 .PHONY: flake8
 flake8:
-	flake8 src setup.py
+	tox -e flake8
 
 include release.mk

ghcloneall.py

@@ -11,21 +11,15 @@
 import subprocess
 import sys
 import threading
+from concurrent import futures
 from operator import itemgetter
 
 try:
-    # Python 3
+    # Python 2
     from ConfigParser import SafeConfigParser as ConfigParser
 except ImportError:  # pragma: PY3
-    # Python 2
-    from configparser import ConfigParser
-
-try:
     # Python 3
-    from concurrent import futures
-except ImportError:  # pragma: PY2
-    # Python 2 backport
-    import futures
+    from configparser import ConfigParser
 
 import requests
 import requests_cache

tox.ini

@@ -16,6 +16,20 @@ commands =
     coverage run -m pytest {posargs}
     coverage report -m --fail-under=100
 
+[testenv:coverage-py2]
+basepython = python2
+deps = {[testenv:coverage]deps}
+commands = {[testenv:coverage]commands}
+
+[testenv:coverage-pypy]
+basepython = pypy
+deps = {[testenv:coverage]deps}
+commands = {[testenv:coverage]commands}
+
+[testenv:coverage-pypy3]
+basepython = pypy3
+deps = {[testenv:coverage]deps}
+commands = {[testenv:coverage]commands}
 
 [testenv:flake8]
 deps = flake8