Merge pull request AsyncHttpClient#1164 from malaporte/fix-npe-in-jdk-proxy

Fix proxy when using JDK provider

Author: slandelle

src/main/java/com/ning/http/client/providers/jdk/JDKAsyncHttpProvider.java

@@ -476,7 +476,6 @@ private void configure(Uri uri, HttpURLConnection urlConnection, Request request
             ProxyServer proxyServer = ProxyUtils.getProxyServer(config, request);
             boolean avoidProxy = ProxyUtils.avoidProxy(proxyServer, uri.getHost());
             if (!avoidProxy) {
-                urlConnection.setRequestProperty("Connection", ka);
                 if (proxyServer.getPrincipal() != null) {
                     urlConnection.setRequestProperty("Proxy-Authorization", AuthenticatorUtils.computeBasicAuthentication(proxyServer));
                 }