fix broken links (#3948)

Author: mairaw

xml/System.IO.Pipes/PipesAclExtensions.xml

@@ -85,10 +85,10 @@
         <param name="pipeSecurity">The security information to apply to the pipe stream.</param>
         <summary>Changes the security attributes of an existing pipe stream.</summary>
         <remarks>To be added.</remarks>
-        <exception cref="ArgumentNullException">
+        <exception cref="System.ArgumentNullException">
           <paramref name="pipeSecurity" /> is <see langword="null" />.
         </exception>
-        <exception cref="IOException">
+        <exception cref="System.IO.IOException">
           <paramref name="stream" /> is a disconnected <see cref="T:System.IO.Pipes.NamedPipeClientStream" /> instance.
         </exception>
       </Docs>