ArrayFormatter now returns arrays for has_many :through associations

The array_formatter was always returning  an empty array when associated
objects were called via a `has_many through:` relationship because they
are loaded as a collection, and the collection is always considered
empty.

resolves: https://github.com/awesome-print/awesome_print/issues/331

CHANGELOG.md

@@ -1,5 +1,5 @@
 ## master (unreleased)
-  - new things!
+  - ArrayFormatter now returns arrays for has_many :through associations [@chadh13] - [#332]
 
 ## 1.8.0
   - stat("$HOME/.aprc") once [@kstephens] - [#304]

lib/awesome_print/formatters/array_formatter.rb

@@ -12,7 +12,7 @@ module AwesomePrint
       end
 
       def format
-        if array.empty?
+        if array.length.zero?
           '[]'
         elsif methods_array?
           methods_array