Updated webserver/frontend field to 'Jetty' (#2608)

Dropwizard is using using Jetty for the HTTP. More info here: http://www.dropwizard.io/1.0.6/docs/getting-started.html#jetty-for-http

frameworks/Java/dropwizard/benchmark_config.json

@@ -18,7 +18,7 @@
       "flavor": "None",
       "orm": "Full",
       "platform": "JAX-RS",
-      "webserver": "None",
+      "webserver": "Jetty",
       "os": "Linux",
       "database_os": "Linux",
       "display_name": "Dropwizard",
@@ -40,7 +40,7 @@
       "flavor": "None",
       "orm": "Full",
       "platform": "JAX-RS",
-      "webserver": "None",
+      "webserver": "Jetty",
       "os": "Linux",
       "database_os": "Linux",
       "display_name": "Dropwizard",
@@ -62,7 +62,7 @@
       "flavor": "None",
       "orm": "Full",
       "platform": "JAX-RS",
-      "webserver": "None",
+      "webserver": "Jetty",
       "os": "Linux",
       "database_os": "Linux",
       "display_name": "dropwizard",
@@ -70,4 +70,4 @@
       "versus": "servlet"
     }
   }]
-}
+}