tox: Update hypothesis to 1.11.2.

Bug fixes:

- Settings(database=my_db) would not be correctly inherited when used as a
  default setting, so that newly created settings would use the database_file
  setting and create an SQLite example database.
- Settings.default.database = my_db would previously have raised an error and
  now works.
- Timeout could sometimes be significantly exceeded if during simplification
  there were a lot of examples tried that didn't trigger the bug.
- When loading a heavily simplified example using a basic() strategy from the
  database this could cause Python to trigger a recursion error.
- Remove use of deprecated API in pytest plugin so as to not emit warning

Misc:

- hypothesis-pytest is now part of hypothesis core. This should have no
  externally visible consequences, but you should update your dependencies to
  remove hypothesis-pytest and depend on only Hypothesis.
- Better repr for hypothesis.extra.datetimes() strategies.
- Add .close() method to abstract base class for Backend (it was already
  present in the main implemnetation).

tox.ini

@@ -21,8 +21,7 @@ deps =
     pytest-qt==1.7.0
     pytest-mock==0.7.0
     pytest-html==1.6
-    hypothesis==1.11.1
+    hypothesis==1.11.2
-    hypothesis-pytest==0.18.1
     coverage==4.0.0
     pytest-cov==2.1.0
     beautifulsoup4==4.4.0