Adding patch to Travis CI for Python 3.7 support

.travis.yml

@@ -11,6 +11,13 @@ python:
   - 3.7
   - pypy
 
+# Travis CI support for Python 3.7 currently requires patch (https://github.com/travis-ci/travis-ci/issues/9815)
+matrix:
+  include:
+    - python: 3.7
+      dist: xenial
+      sudo: true
+
 env:
   - BUILD_CAPNP=
   - BUILD_CAPNP=true