Fix typo in Path.xml (#5003)

Author: kapsiR

xml/System.IO/Path.xml

@@ -655,7 +655,7 @@ When you are using .NET Core to develop applications that run on multiple platfo
    path = $"{separator}users{separator}user1{separator}"
    ``` 
 
-   You can also retrieve the value from the <xref:System.IO.Path.AltDirectorySeparatorChar> property, since it is the same on both Windows and Unx-based systems.
+   You can also retrieve the value from the <xref:System.IO.Path.AltDirectorySeparatorChar> property, since it is the same on both Windows and Unix-based systems.
 
 - Retrieve the <xref:System.IO.Path.AltDirectorySeparatorChar> property