doc: fix code syntax

Add a ';' to the end of a function call in documentation.

PR-URL: https://github.com/joyent/node/pull/9198
Reviewed-by: Trevor Norris <trev.norris@gmail.com>

doc/api/fs.markdown

@@ -29,7 +29,7 @@ Here is the synchronous version:
 
     var fs = require('fs');
 
-    fs.unlinkSync('/tmp/hello')
+    fs.unlinkSync('/tmp/hello');
     console.log('successfully deleted /tmp/hello');
 
 With the asynchronous methods there is no guaranteed ordering. So the