express-server-test: Fix proxy tests

node v0.10.42 is rejecting DELETE requests with both Content-Length: 0 and
Transfer-Encoding: chunked headers. We can force Content-Length: 0 to work
around the problem.

see http-party/node-http-proxy#960
and ladjs/superagent#236

Author: Turbo87

tests/unit/tasks/server/express-server-test.js

@@ -281,6 +281,7 @@ describe('express-server', function() {
       function apiTest(app, method, url, done) {
         var req = request(app);
         return req[method].call(req, url)
+          .set('content-length', 0)
           .set('accept', 'text/json')
           .end(function(err) {
             if (err) {