[lock.json] 'active_profile' -> 'current_profile_name' #74

$ bin/volt help migrate

Usage
  volt migrate

Description
    Perform migration of $VOLTPATH/lock.json, which means volt converts old version lock.json structure into the latest version. This is always done automatically when reading lock.jso
n content. For example, 'volt get <repos>' will install plugin, and migrate lock.json structure, and write it to lock.json after all. so the migrated content is written to lock.json au
tomatically.
    But, for example, 'volt list' does not write to lock.json but does read, so every time when running 'volt list' shows warning about lock.json is old.
    To suppress this, running this command simply reads and writes migrated structure to lock.json.