Add definition 5.4.21 - #158

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>
Chmod +x definition 5.4.21 - #158

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>
Update STABLE_DEFINITIONS with 5.4.21 - #158

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>
Update travis.yml to run 5.4.21 - #158

Fix #158: Need definition for 5.5.5 and 5.4.21

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>