tox: Update hypothesis to 1.10.3.

Upstream changelog:

* lists(elements, unique_by=some_function, min_size=n) would have raised a
  ValidationError if n > Settings.default.average_list_length because it would
  have wanted to use an average list length shorter than the minimum size of
  the list, which is impossible. Now it instead defaults to twice the minimum
  size in these circumstances.
* basic() strategy would have only ever produced at most ten distinct values
  per run of the test (which is bad if you e.g. have it inside a list). This
  was obviously silly. It will now produce a much better distribution of data,
  both duplicated and non duplicated.
* star imports from hypothesis should now work correctly.
* example quality for examples using flatmap will be better, as the way it had
  previously been implemented was causing problems where Hypothesis was
  erroneously labelling some examples as being duplicates.

tox.ini

@@ -20,7 +20,7 @@ deps =
     pytest-qt==1.5.1
     pytest-mock==0.7.0
     pytest-html==1.5.1
-    hypothesis==1.10.1
+    hypothesis==1.10.3
     hypothesis-pytest==0.17.0
     coverage==3.7.1
     pytest-cov==2.0.0