Do not require dev version of mongodb

[danez]

When explicitely requiring a dev version of mongodb, this can conflict with project setups, that have a minimum-stability of stable.

Problem 1
    - Installation request for iampersistent/mongodb-acl-bundle dev-master@dev -> satisfiable by iampersistent/mongodb-acl-bundle[dev-master].
    - iampersistent/mongodb-acl-bundle dev-master requires doctrine/mongodb 1.0.x-dev -> no matching package found.

I think it is better to require a minimum version of ~1.0 which has to advantages:

• You can install stable versions in project (or let composer choose the latest matching stable) or require 1.0.x-dev
• You can install 1.1.* versions which is also not possible currently

Also adding minimum-stability in a library/bundle is only useful for unit-tests, but testing against stable versions is not wrong imho.

Also changed the version of symfony/security to a shorter one, that is doing the same thing.