http_proxy is optional configuration, handle if it doesn't exist

lib/primary.js

@@ -110,8 +110,9 @@ exports.checkSupport = function(domain, cb) {
     });
   };
 
-  // now we need to check to see if domain purports to being a primary for browserid
-  var httpProxy = config.get('http_proxy');
+  // now we need to check to see if domain purports to being a primary
+  // for browserid
+  var httpProxy = config.has('http_proxy') ? config.get('http_proxy') : null;
 
   var req;
   if (httpProxy && httpProxy.port && httpProxy.host) {