Dropped support for Ruby <= 1.9.2
Changed how we merge array values in bag
 * The default is to replace current by merged one.
 * Added :array_strategy option to merge! to change this default
   behavior, not sure how it will be integrated with Vagrant yet.
Removed deprecated --script argument for env command
Added restricted-keys command and documented keys restriction
Some elements cleanup and fixed a parameters command
Using a mixin for Parameters
 * The mixin reduce duplication between standard Nugrant::Parameters
   and Vagrant Config object which is also a Parameters.
Improved vagrant user parameters command
 * We now prints a warning when restricted keys are defined.
Improved readability a big of Bag's constructor
Moved restricted keys warning between vm name and bag type