gpgme-tool: Fix chain_id -> chain-id in KEYLIST XML.
src/gpgme-tool.c (cmd_keylist): Use <chain-id> instead of <chain_id>.
All the other tags map struct attribute underscores to hyphens, so
fixing <chain_id> follows the priciple of least surprise.
- Signed-off-by: W. Trevor King <wking@tremily.us>