Upgrade ekka lib to 0.19.5

ekka 0.19.5 uses mria 0.8.8 that improves auto-heal functionality.
Previously, the auto-heal worked only when all core nodes were reachable again.
This update allows to apply auto-heal once the majority of core nodes are alive. 

[Mria PR](https://github.com/emqx/mria/pull/180)