Fix numpy version

TestIntArray.test_bad_values fails with numpy>=1.16.0,
so it makes sense to pin numpy to <1.16.0 for now.

These changes also:

 - Make CI update requirements

 - Add pip freeze command to CI install step

Author: Jamim

.travis.yml

@@ -6,7 +6,8 @@ python:
 sudo: false
 install:
     - pip install -U pip
-    - pip install ".[test]" coveralls
+    - pip install -U --upgrade-strategy eager ".[test]" coveralls
+    - pip freeze
 script:
     - nosetests --with-coverage --cover-package traittypes traittypes
 after_success:

setup.py

@@ -83,7 +83,9 @@
 
 extras_require = setuptools_args['extras_require'] = {
     'test': [
-        'numpy',
+        # TestIntArray.test_bad_values fails with numpy>=1.16.0
+        'numpy<1.16.0',
+
         'pandas',
         'xarray',
         'pytest',  # traitlets[test] require this