AS guide: fixes an example

railties/guides/source/active_support_core_extensions.textile

@@ -888,7 +888,7 @@ Similarly, +from+ returns the tail from the element at the passed index on:
 <ruby>
 %w(a b c d).from(2)  # => %w(c d)
 %w(a b c d).from(10) # => nil
-[].from(0)           # => nil
+[].from(0)           # => []
 </ruby>
 
 The methods +second+, +third+, +fourth+, and +fifth+ return the corresponding element (+first+ is builtin). Thanks to social wisdom and positive constructiveness all around, +forty_two+ is also available.