Fix typo on System.IO.Path API docs (#2372)

Author: dahlia

xml/System.IO/Path.xml

@@ -922,7 +922,7 @@ The returned value is `null` if the file path is `null`.
   
 The separator characters used to determine the start of the file name are <xref:System.IO.Path.DirectorySeparatorChar> and <xref:System.IO.Path.AltDirectorySeparatorChar>.  
 
-Because *\\* is a legal file name on Unix, `GetFileName` running under Unix-based platforms cannot correctly return the file name from a Windows=based path like *C:\\mydir\\myfile.ext*, but `GetFileName` running under Windows-based platforms can correctly return the file name from a Unix-based path like */tmp/myfile.ext*, so the behavior of the `GetFileName` method is not strictly the same on Unix-based and Windows-based platforms.
+Because *\\* is a legal file name on Unix, `GetFileName` running under Unix-based platforms cannot correctly return the file name from a Windows-based path like *C:\\mydir\\myfile.ext*, but `GetFileName` running under Windows-based platforms can correctly return the file name from a Unix-based path like */tmp/myfile.ext*, so the behavior of the `GetFileName` method is not strictly the same on Unix-based and Windows-based platforms.
 
 For a list of common I/O tasks, see [Common I/O Tasks](~/docs/standard/io/common-i-o-tasks.md).