Disable MyGet preview feeds (#1285)

Author: paulirwin

NuGet.config

@@ -21,8 +21,8 @@ under the License.
 
 <configuration>
   <packageSources>
-    <add key="ICU4N preview feed" value="https://www.myget.org/F/icu4n/api/v3/index.json" />
-    <add key="J2N preview feed" value="https://www.myget.org/F/j2n-preview/api/v3/index.json" />
+    <!-- <add key="ICU4N preview feed" value="https://www.myget.org/F/icu4n/api/v3/index.json" /> -->
+    <!-- <add key="J2N preview feed" value="https://www.myget.org/F/j2n-preview/api/v3/index.json" /> -->
     <add key="NuGet official package source" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>