Update fopen.xml for 'n' flag (php#2718)

PHP has supported fopen with `'n'` since 2013. Document this.

Author: kohler

reference/filesystem/functions/fopen.xml

@@ -190,7 +190,14 @@ $handle = fopen("c:\\folder\\resource.txt", "r");
            <entry><literal>'e'</literal></entry>
            <entry>
             Set close-on-exec flag on the opened file descriptor. Only
-            available in PHP compiled on POSIX.1-2008 conform systems.
+            available in PHP compiled on POSIX.1-2008 conformant systems.
+           </entry>
+          </row>
+          <row>
+           <entry><literal>'n'</literal></entry>
+           <entry>
+            Set non-blocking flag on the opened file descriptor. Only
+            available in PHP compiled on POSIX.1-2008 conformant systems.
            </entry>
           </row>
          </tbody>