Don't generate NaNs.

JSON doesn't actually allow these (despite the json module in Python happily
serializing / parsing 'nan'), and they make assertEqual fail since they're not
equal to anything, including themselves.

Author: mithrandi

tests.py

@@ -524,7 +524,7 @@ def test_replace_missing(self):
     st.one_of([
         st.none(),
         st.booleans(),
-        st.floats(),
+        st.floats(allow_nan=False),
         st.text(string.printable)]),
     lambda children:
     st.lists(children)