Use master of root_numpy for Python 3.7

Author: chrisburr

.travis.yml

@@ -20,6 +20,11 @@ install:
   - conda create -q -n testenv python=${PYTHON} nomkl root pandas nose
   - export CONDA_ENV_PATH=$HOME/miniconda/envs/testenv
   - source activate testenv
+  - if [ "${PYTHON}" == "3.7" ]; then
+      pip install git+https://github.com/scikit-hep/root_numpy.git
+    else
+      pip install root_numpy
+    fi
   - pip install root_numpy rootpy
   - pip install coverage coveralls