fix(package): update semver to version 6.0.0

Closes #37

Author: greenkeeper[bot]

package.json

@@ -90,7 +90,7 @@
     "node-core-module-names": "^1.1.0",
     "request": "^2.83.0",
     "request-promise": "^4.2.2",
-    "semver": "^5.5.0"
+    "semver": "^6.0.0"
   },
   "repository": {
     "type": "git",