fix(package): update pg-promise to version 6.2.0

Closes #18

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
     "listify": "^1.0.0",
     "node-pg-migrate": "^1.1.0",
     "pg-connection-string": "^0.1.3",
-    "pg-promise": "^5.6.2",
+    "pg-promise": "^6.2.0",
     "request-promise": "^4.1.1",
     "socket.io": "^2.0.0",
     "tmi.js": "^1.1.2",