Fix header name

lib/document_handler.js

@@ -69,7 +69,7 @@ DocumentHandler.prototype.handlePost = function (request, response) {
     _this.chooseKey(function (key) {
       _this.store.set(key, buffer, function (res) {
         if (res) {
-          var ip = request.headers['X-Forwarded-For'] || request.ip;
+          var ip = request.headers['x-forwarded-for'] || request.ip;
           winston.verbose('added document', { key: key, ip: ip });
           response.writeHead(200, { 'content-type': 'application/json' });
           response.end(JSON.stringify({ key: key }));