[fix] perf optimization so we have a precompiled regexp

Author: jcrugzz

lib/http-proxy/common.js

@@ -2,6 +2,7 @@ var common = exports,
     url    = require('url'),
     extend = require('util')._extend;
 
+var upgradeHeader = /(^|,)\s*upgrade\s*($|,)/i;
 /**
  * Copies the right headers from `options` and `req` to
  * `outgoing` which is then used to fire the proxied
@@ -53,7 +54,7 @@ common.setupOutgoing = function(outgoing, options, req, forward) {
   if (!outgoing.agent) {
     outgoing.headers = outgoing.headers || {};
     if (typeof outgoing.headers.connection !== 'string'
-        || ! /(^|,)\s*upgrade\s*($|,)/i.test(outgoing.headers.connection)
+        || ! upgradeHeader.test(outgoing.headers.connection)
        ) { outgoing.headers.connection = 'close'; }
   }