Update _example/mod_regexp to remove memory leak in regexp_func

[Binary-Eater]

Valgrind report before the change.

==13662== LEAK SUMMARY:
==13662==    definitely lost: 87 bytes in 1 blocks
==13662==    indirectly lost: 0 bytes in 0 blocks
==13662==      possibly lost: 1,152 bytes in 4 blocks
==13662==    still reachable: 0 bytes in 0 blocks
==13662==         suppressed: 0 bytes in 0 blocks

Valgrind report after the change.

==10847== LEAK SUMMARY:
==10847==    definitely lost: 0 bytes in 0 blocks
==10847==    indirectly lost: 0 bytes in 0 blocks
==10847==      possibly lost: 1,152 bytes in 4 blocks
==10847==    still reachable: 0 bytes in 0 blocks
==10847==         suppressed: 0 bytes in 0 blocks