xmlDoc is a build option

Author: JunTaoLuo

src/Microsoft.AspNetCore.ResponseCaching/project.json

@@ -5,7 +5,8 @@
     "keyFile": "../../tools/Key.snk",
     "nowarn": [
       "CS1591"
-    ]
+    ],
+    "xmlDoc": true
   },
   "description": "ASP.NET Core middleware for caching HTTP responses on the server.",
   "packOptions": {
@@ -17,8 +18,7 @@
       "aspnetcore",
       "cache",
       "caching"
-    ],
-    "xmlDoc": true
+    ]
   },
   "dependencies": {
     "Microsoft.AspNetCore.Http": "1.1.0-*",