Add spec to cover Badge Type has many Badges relation

Also: fix filename. `_spec` suffix was missing.
By default, RSpec ignores files in this situation.
Ref: https://github.com/rspec/rspec-core/issues/642

spec/models/badge_type_spec.rb

@@ -3,7 +3,7 @@ require_dependency 'badge_type'
 
 describe BadgeType do
 
+  it { is_expected.to have_many :badges }
   it { is_expected.to validate_presence_of :name }
   it { is_expected.to validate_uniqueness_of :name }
-
 end