Fix unescaped backslash (#4136)

Author: loganrosen

xml/System.IO.Enumeration/FileSystemName.xml

@@ -54,7 +54,7 @@
         <param name="name">The name to check against the expression.</param>
         <param name="ignoreCase">
           <see langword="true" /> to ignore case (default); <see langword="false" /> if the match should be case-sensitive.</param>
-        <summary>Verifies if the given expression matches the given name. Supports the following wildcards: '*' and '?'. The backslash character '\' escapes.</summary>
+        <summary>Verifies if the given expression matches the given name. Supports the following wildcards: '*' and '?'. The backslash character '\\' escapes.</summary>
         <returns>
           <see langword="true" /> if the given expression matches the given name; otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>