Custom JQL functions don't auto-recompile on execution

To reproduce:

• Create a custom JQL function following the instructions in the docs, then scan for it.
• Use the function in a JQL query in the Issue Explorer to verify that it works.
• Modify the function's source file in a way that would change its behaviour.
• Without re-scanning, use the function in a query again.

Expected result: The function behaves in the new way.

Actual result: The function behaves as it did before.