Inherit generator priority from builder

* BREAKING CHANGE (maybe?): the exact order multiple generators will run in may be subtly different than before. Use Builder priorities to resolve

bridgetown-builder/lib/bridgetown-builder/dsl/generators.rb

@@ -7,13 +7,16 @@ module Generators
         def generator(method_name = nil, &block)
           block = method(method_name) if method_name.is_a?(Symbol)
           local_name = name # pull the name method into a local variable
+          builder_priority = self.class.instance_variable_get(:@priority)
 
-          new_gen = Class.new(Bridgetown::Generator) do
+          anon_generator = Class.new(Bridgetown::Generator) do
             define_method(:_builder_block) { block }
             define_singleton_method(:custom_name) { local_name }
 
             attr_reader :site
 
+            priority builder_priority || :low
+
             def inspect
               "#<#{self.class.custom_name} (Generator)>"
             end
@@ -23,10 +26,10 @@ def generate(_site)
             end
           end
 
-          first_low_priority_index = site.generators.find_index { |gen| gen.class.priority == :low }
-          site.generators.insert(first_low_priority_index || 0, new_gen.new(site.config))
+          site.generators << anon_generator.new(site.config)
+          site.generators.sort!
 
-          functions << { name: name, generator: new_gen }
+          functions << { name: name, generator: anon_generator }
         end
       end
     end

bridgetown-builder/test/test_generators.rb

@@ -13,6 +13,8 @@ def build
 end
 
 class GeneratorBuilder2 < Builder
+  priority :normal
+
   def build
     generator do
       site.data[:site_metadata][:title] = "Test Title 2"