py37 fixes (#646)

* add python version for nightly build

* update numpy version required

older versions interact poorly on anaconda + python 3.7

.travis.yml

@@ -22,6 +22,7 @@ jobs:
     python: "3.6"
     script: ./travis-build.sh
   - name: "Smoke Tests"
+    python: "3.6"
     if: branch = master AND type = cron
     script:
       - npm run --prefix client/ smoke-test

server/requirements.txt

@@ -7,7 +7,7 @@ Flask-Cors>=3.0.6
 Flask-RESTful>=0.3.6
 flatbuffers>=1.10.0
 matplotlib>=2.2
-numpy>=1.14.5
+numpy>=1.15.2
 pandas>=0.23.1
 scanpy>=1.3.2
 scipy>=1.1.0