chore(package): update npm to version 6.13.0

Closes #32

Author: greenkeeper[bot]

package.json

@@ -72,7 +72,7 @@
     "nodeos-cross-toolchain": "^1.0.0-RC3.1",
     "nodeos-nodejs": "^8.4.0",
     "nodeos-reverse-proxy": "^0.1.1",
-    "npm": "^5.8.0",
+    "npm": "^6.13.0",
     "bin-nsh": "^0.5.2",
     "ntp-client": "^0.5.3",
     "palmtree": "^2.6.0",