tox: Update hypothesis to 3.1.0

- Add a 'nothing' strategy that never successfully generates values.
- sampled_from() and one_of() can both now be called with an empty argument
  list, in which case they also never generate any values.
- one_of may now be called with a single argument that is a collection of
  strategies as well as as varargs.
- Add a 'runner' strategy which returns the instance of the current test object
  if there is one.
- 'Bundle' for RuleBasedStateMachine is now a normal(ish) strategy and can be
  used as such.
- Tests using RuleBasedStateMachine should now shrink significantly better.
- Hypothesis now uses a pretty-printing library internally, compatible with
  IPython's pretty printing protocol (actually using the same code). This may
  improve the quality of output in some cases.
- As a 'phases' setting that allows more fine grained control over which parts
  of the process Hypothesis runs
- Add a suppress_health_check setting which allows you to turn off specific
  health checks in a fine grained manner.
- Fix a bug where lists of non fixed size would always draw one more element
  than they included. This mostly didn't matter, but if would cause problems
  with empty strategies or ones with side effects.
- Add a mechanism to the Django model generator to allow you to explicitly
  request the default value (thanks to Jeremy Thurgood for this one).

tox.ini

@@ -20,7 +20,7 @@ deps =
     Flask==0.10.1
     glob2==0.4.1
     httpbin==0.4.1
-    hypothesis==3.0.5
+    hypothesis==3.1.0
     itsdangerous==0.24
     Mako==1.0.3
     parse==1.6.6