merge once signed-off (#20)
merge once signed-off (#20)

This PR changes Mergify with the following rules for automatic merge (squash): 

* merge if at least one sign-off
* all requested reviewers have signed
* build is green
* not block-merge
* nobody requested for change

If nobody is assigned as reviewer, we still need someone to come voluntarily and review it. If we ask review, for instance, two 2 maintainers, the two must come and sign-off. 


rcavalcanti/lagom,ignasi35/lagom,rcavalcanti/lagom,TimMoore/lagom,lagom/lagom,ignasi35/lagom,lagom/lagom,TimMoore/lagom,lagom/lagom,TimMoore/lagom,rcavalcanti/lagom,lagom/lagom,ignasi35/lagom,ignasi35/lagom,rcavalcanti/lagom,TimMoore/lagom,lagom/lagom,TimMoore/lagom,ignasi35/lagom