Use webserver=HTTP.sys for HttpListener

As described in #558, use this labeling instead of IIS.

HttpListener/benchmark_config

@@ -13,7 +13,7 @@
       "language": "C#",
       "orm": "Raw",
       "platform": "NET",
-      "webserver": "IIS",
+      "webserver": "HTTP.sys",
       "os": "Windows",
       "database_os": "Linux",
       "display_name": "http-listener",
@@ -34,7 +34,7 @@
       "language": "C#",
       "orm": "Raw",
       "platform": "NET",
-      "webserver": "IIS",
+      "webserver": "HTTP.sys",
       "os": "Windows",
       "database_os": "Linux",
       "display_name": "http-listener",
@@ -55,7 +55,7 @@
       "language": "C#",
       "orm": "Raw",
       "platform": "NET",
-      "webserver": "IIS",
+      "webserver": "HTTP.sys",
       "os": "Windows",
       "database_os": "Linux",
       "display_name": "http-listener",
@@ -76,7 +76,7 @@
       "language": "C#",
       "orm": "Raw",
       "platform": "NET",
-      "webserver": "IIS",
+      "webserver": "HTTP.sys",
       "os": "Windows",
       "database_os": "Linux",
       "display_name": "http-listener",
@@ -97,7 +97,7 @@
       "language": "C#",
       "orm": "Raw",
       "platform": "NET",
-      "webserver": "IIS",
+      "webserver": "HTTP.sys",
       "os": "Windows",
       "database_os": "Windows",
       "display_name": "http-listener",