Moo versions before 1.00600 cause test failures

[jwrightecs]

Moo before 1.00600 lacks the 'coerce => 1' feature for attributes

t/unit/00-load.t ............................. 1/? Bailout called.  Further testing stopped:  

#   Failed test 'use WebService::Braintree;'
#   at t/unit/00-load.t line 11.
#     Tried to use 'WebService::Braintree'.
#     Error:  Invalid coerce '1' for WebService::Braintree::_::AmexExpressCheckoutCard->subscriptions not a coderef or code-convertible object at /home/perl/perl5/lib/perl5/Method/Generate/Accessor.pm line 642.