fix(deps): update socket.io to version 2.0.3

This is a duplicate of @kevinsalter PR #2821. His PR fails on appveyor and we can't figure out how to change the repo config to fix the build there or how to retry that build.  So let's just try from scratch.

Fixes issue #2777

package.json

@@ -350,7 +350,7 @@
     "range-parser": "^1.2.0",
     "rimraf": "^2.6.0",
     "safe-buffer": "^5.0.1",
-    "socket.io": "1.7.4",
+    "socket.io": "2.0.3",
     "source-map": "^0.5.3",
     "tmp": "0.0.31",
     "useragent": "^2.1.12"