Use major + minor AR versions in 'Directly inheriting' error message

activerecord/lib/active_record/migration.rb

@@ -556,10 +556,12 @@ module ActiveRecord
     def self.inherited(subclass) #:nodoc:
       super
       if subclass.superclass == Migration
+        major = ActiveRecord::VERSION::MAJOR
+        minor = ActiveRecord::VERSION::MINOR
         raise StandardError, "Directly inheriting from ActiveRecord::Migration is not supported. " \
-          "Please specify the Rails release the migration was written for:\n" \
+          "Please specify the Active Record release the migration was written for:\n" \
           "\n" \
-          "  class #{subclass} < ActiveRecord::Migration[4.2]"
+          "  class #{subclass} < ActiveRecord::Migration[#{major}.#{minor}]"
       end
     end
 

activerecord/test/cases/migration/compatibility_test.rb

@@ -204,7 +204,7 @@ module ActiveRecord
         e = assert_raises(StandardError) do
           class_eval("class LegacyMigration < ActiveRecord::Migration; end")
         end
-        assert_match(/LegacyMigration < ActiveRecord::Migration\[4\.2\]/, e.message)
+        assert_match(/LegacyMigration < ActiveRecord::Migration\[\d\.\d\]/, e.message)
       end
 
       def test_legacy_migrations_not_raise_exception_on_reverting_transaction