Update version to 2.0.0 as '2.0' breaks Composer extensions that require '2.0.0', e.g.

"require" : {
    "bolt/bolt" : ">=2.0.0,<3.0.0"
},
CommandRunner constructor no longer needs the asterix on $app['bolt_version']
Merge pull request #1538 from GawainLynch/hotfix/bolt-version

Update version to 2.0.0 as '2.0' breaks Composer extensions "require"