Install numpy from manylinux binary wheel on Travis
diff --git a/.travis.yml b/.travis.yml
index 18177a2..3f9cb50 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,6 +26,7 @@
       install:
         - pyvenv-3.5 venv
         - source venv/bin/activate
+        - pip install -U pip wheel
         - pip install numpy
       script:
         - CXX=g++-4.8 cmake -DPYBIND11_PYTHON_VERSION=3.5