chore(package): update socket.io to version 1.7.3

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "convict": "^2.0.0",
     "express": "^4.14.1",
     "request-promise": "^4.1.1",
-    "socket.io": "^1.7.2",
+    "socket.io": "^1.7.3",
     "tmi.js": "^1.1.2",
     "winston": "^2.3.0"
   },