fix maxRequestLength value

Author: shishirx34

src/NuGet.Server/Web.config

@@ -66,7 +66,7 @@
       </system.Web>
   -->
   <system.web>
-    <httpRuntime maxRequestLength="31457280" />
+    <httpRuntime maxRequestLength="30720" />
     <compilation debug="true" targetFramework="4.6" />
   </system.web>
   <system.serviceModel>