Remove legacy conditional check

`parent` was needed to support Active Model 5. Since the minimum
required version is not 7, the conditional is not needed anymore

Close #12

lib/hawk/linker.rb

@@ -37,7 +37,7 @@ def _monomorphic_resource_accessor(entity, options)
  def #{entity}
  return nil unless self.#{key}.present?
 
- @_#{entity} ||= #{respond_to?(:module_parent) ? module_parent : parent}::#{klass}.find(self.#{key})
+ @_#{entity} ||= #{module_parent}::#{klass}.find(self.#{key})
  end
  RUBY
 

lib/hawk/model/lookup.rb

@@ -66,7 +66,7 @@ def look_up_model_class(name, scope)
  return self_constant
  end
 
- scope_parent = scope.respond_to?(:module_parent) ? scope.module_parent : scope.parent
+ scope_parent = scope.module_parent
 
  if (parent_constant = look_up_constant_in(name, scope_parent))
  return parent_constant
@@ -82,11 +82,7 @@ def look_up_model_class(name, scope)
  end
 
  def look_up_constant_in(name, scope)
- if scope.respond_to?(:module_parent)
- scope.module_parent.const_get(name)
- else
- scope.parent.const_get(name)
- end
+ scope.module_parent.const_get(name)
  rescue NameError
  nil
  end