Updated assert_contains and assert_does_not_contain to work with …

…more objects that quack like an Array

Closes https://github.com/thoughtbot/shoulda/issues/#issue/139

lib/shoulda/context/assertions.rb

@@ -22,7 +22,7 @@ def assert_same_elements(a1, a2, msg = nil)
       #   assert_contains(['a', '1'], 'a') => passes
       #   assert_contains(['a', '1'], /not there/) => fails
       def assert_contains(collection, x, extra_msg = "")
-        collection = [collection] unless collection.is_a?(Array)
+        collection = Array(collection)
         msg = "#{x.inspect} not found in #{collection.to_a.inspect} #{extra_msg}"
         case x
         when Regexp
@@ -35,7 +35,7 @@ def assert_contains(collection, x, extra_msg = "")
       # Asserts that the given collection does not contain item x.  If x is a regular expression, ensure that
       # none of the elements from the collection match x.
       def assert_does_not_contain(collection, x, extra_msg = "")
-        collection = [collection] unless collection.is_a?(Array)
+        collection = Array(collection)
         msg = "#{x.inspect} found in #{collection.to_a.inspect} " + extra_msg
         case x
         when Regexp