Fix ActiveSupport Cache decrement method description

activesupport/lib/active_support/cache.rb

@@ -405,7 +405,7 @@ def increment(name, amount = 1, options = nil)
         raise NotImplementedError.new("#{self.class.name} does not support increment")
       end
 
-      # Increment an integer value in the cache.
+      # Decrement an integer value in the cache.
       #
       # Options are passed to the underlying cache implementation.
       #