update migration generator test to rely on config table name

should we do this though? i can see an argument where we actually keep the test as is because the default `table_name` is still `key_values` and we're trying to maintain original usage expectations with this PR

test/generators/github/store/active_record_generator_test.rb

@@ -17,24 +17,25 @@ class GithubDSActiveRecordGeneratorTest < Rails::Generators::TestCase
     else
       "[#{Rails::VERSION::MAJOR}.#{Rails::VERSION::MINOR}]"
     end
+    table_name = "key_values"
     assert_migration "db/migrate/create_key_values_table.rb", <<-EOM
 class CreateKeyValuesTable < ActiveRecord::Migration#{migration_version}
   def self.up
-    create_table :key_values do |t|
+    create_table :#{table_name} do |t|
       t.string :key, :null => false
       t.binary :value, :null => false
       t.datetime :expires_at, :null => true
       t.timestamps :null => false
     end
 
-    add_index :key_values, :key, :unique => true
+    add_index  :#{table_name}, :key, :unique => true
-    add_index :key_values, :expires_at
+    add_index  :#{table_name}, :expires_at
 
-    change_column :key_values, :id, "bigint(20) NOT NULL AUTO_INCREMENT"
+    change_column  :#{table_name}, :id, "bigint(20) NOT NULL AUTO_INCREMENT"
   end
 
   def self.down
-    drop_table :key_values
+    drop_table  :#{table_name}
   end
 end
 EOM