Update min tox version to 2.0

huang.zhiping · huang.zhiping · commit 81dd80922c87 · 2018-10-21T02:20:04.000Z
The commands used by constraints need at least tox 2.0.  Update to
reflect reality, which should help with local running of constraints
targets.

Change-Id: I8146e56453c518f8d8ae822157c1e4931708959a
diff --git a/tox.ini b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-minversion = 1.6
+minversion = 2.0
 skipsdist = True
 envlist = py{34,27,35}, linters, pypy
 
