fix(package): update cross-env to version 6.0.2

Closes #60

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "bvh": "git+https://github.com/hitsujiwool/bvh.git",
     "clui": "^0.3.6",
     "colors": "^1.1.2",
-    "cross-env": "^5.1.3",
+    "cross-env": "^6.0.2",
     "d3-node": "^1.1.3",
     "debug": "^3.1.0",
     "fast-csv": "^2.4.1",