remove unused local variables

lib/database_cleaner/base.rb

@@ -128,7 +128,7 @@ module DatabaseCleaner
     def orm_strategy(strategy)
       require "database_cleaner/#{orm.to_s}/#{strategy.to_s}"
       orm_module.const_get(strategy.to_s.capitalize)
-    rescue LoadError => e
+    rescue LoadError
       if orm_module.respond_to? :available_strategies
         raise UnknownStrategySpecified, "The '#{strategy}' strategy does not exist for the #{orm} ORM!  Available strategies: #{orm_module.available_strategies.join(', ')}"
       else