fix broken link (#3807)

Author: mairaw

xml/System.IO/FileSystemWatcher.xml

@@ -125,7 +125,7 @@
     <altmember cref="T:System.IO.RenamedEventHandler" />
     <altmember cref="T:System.IO.WaitForChangedResult" />
     <altmember cref="T:System.IO.WatcherChangeTypes" />
-    <related type="ExternalDocumentation" href="https://code.msdn.microsoft.com/Using-a-FileSystemWatcher-4bc97af4">Using a FileSystemWatcher Component in a Windows Form</related>
+    <related type="ExternalDocumentation" href="https://github.com/microsoftarchive/msdn-code-gallery-community-s-z/tree/master/Using%20a%20FileSystemWatcher%20Component%20in%20a%20Windows%20Form%20with%20C%23">Using a FileSystemWatcher Component in a Windows Form</related>
   </Docs>
   <Members>
     <MemberGroup MemberName=".ctor">