Update README to specify "bernard/bernard": "dev-master" in composer.json

[robskrob]

When I follow the README and executecomposer require bernard/bernard the version of bernard installed is, bernard/bernard": "^0.13.0". I see Bernard\Router\ReceiverMapRouter exists in master, and the only way I am aware of getting the latest version is if I spell out in my composer file the following "bernard/bernard": "dev-master".

[phpbg]

I guess it would even be better to tag a new release.

See #392

@sagikazarmark any update on making an updated release?

[sagikazarmark]

Please see #413

[pluc]

What is happening with this