test: fix test-http-content-length

Previously the test did not allow the last request to complete.

Fixes: https://github.com/iojs/io.js/pull/1137
PR-URL: https://github.com/iojs/io.js/pull/1145
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Bert Belder <bertbelder@gmail.com>

test/parallel/test-http-content-length.js

@@ -18,7 +18,7 @@ var expectedHeadersEndNoData = {
 };
 
 var receivedRequests = 0;
-var totalRequests = 2;
+var totalRequests = 3;
 
 var server = http.createServer(function(req, res) {
   res.removeHeader('Date');