Merge pull request nteract#1018 from nteract/greenkeeper-cross-env-3.1.3

cross-env@3.1.3 breaks build ⚠️

Author: rgbkrk

package.json

@@ -68,7 +68,7 @@
     "chai-immutable": "^1.6.0",
     "colors": "^1.1.2",
     "command-exists": "^1.0.2",
-    "cross-env": "^3.0.0",
+    "cross-env": "^3.1.3",
     "electron": "1.4.3",
     "electron-builder": "^7.13.0",
     "electron-mocha": "^3.0.6",