Enable CI for Python 3.7 & limit fuzzing

In current hypothesis version there is no longer timeout for test,
so limit of tested examples needs to be matching with CI time limit
for pass test.

.travis.yml

@@ -5,6 +5,7 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
+  - "3.7"
   - "pypy"
   - "pypy3"
 install:

src/icalendar/tests/hypothesis/test_fuzzing.py

@@ -23,7 +23,7 @@ class TestFuzzing(unittest.TestCase):
         st.tuples(key, st.dictionaries(key, value), value),
         min_size=1
     ))
-    @settings(max_examples=10**4)
+    @settings(max_examples=3000)
     def test_main(self, lines):
         cl = Contentlines()
         for key, params, value in lines:

tox.ini

@@ -1,15 +1,15 @@
 # to run for a specific environment, use ``tox -e ENVNAME``
 [tox]
-envlist = py27,py34,py35,py36,pypy,pypy3
+envlist = py27,py34,py35,py36,py37,pypy,pypy3
 
 [testenv]
 deps =
     pytest
     coverage
-    py{27,34,35,36}: hypothesis>=3.0
+    py{27,34,35,36,37}: hypothesis>=3.0
     .[test]
 commands =
     coverage run --source=src/icalendar --omit=*/tests/* --module pytest []
-    py{27,34,35,36}: coverage run --append --source=src/icalendar --omit=*/tests/* --module pytest [] src/icalendar/tests/hypothesis/
+    py{27,34,35,36,37}: coverage run --append --source=src/icalendar --omit=*/tests/* --module pytest [] src/icalendar/tests/hypothesis/
     coverage report
     coverage html