Pass options to along to exists? super calls

Fixes #670

lib/i18n/backend/fallbacks.rb

@@ -95,7 +95,7 @@ def exists?(locale, key, options = EMPTY_HASH)
         return super unless options.fetch(:fallback, true)
         I18n.fallbacks[locale].each do |fallback|
           begin
-            return true if super(fallback, key)
+            return true if super(fallback, key, options)
           rescue I18n::InvalidLocale
             # we do nothing when the locale is invalid, as this is a fallback anyways.
           end

test/backend/fallbacks_test.rb

@@ -312,7 +312,7 @@ class Chain < I18n::Backend::Chain
   def setup
     super
     backend = Backend.new
-    backend.store_translations(:de, :foo => 'FOO')
+    backend.store_translations(:de, :foo => 'FOO', :nested => { key: "value" })
     backend.store_translations(:'pt-BR', :foo => 'Baz in :pt-BR')
     I18n.backend = Chain.new(I18n::Backend::Simple.new, backend)
   end
@@ -325,6 +325,10 @@ def setup
     assert_equal true, I18n.exists?(:foo, :locale => :'de-DE')
   end
 
+  test "exists? passes along the scope option" do
+    assert_equal true, I18n.exists?(:key, :locale => :'de-DE', scope: :nested)
+  end
+
   test "exists? should return false when fallback disabled given a key missing from the given locale" do
     assert_equal false, I18n.exists?(:foo, :locale => :'de-DE', fallback: false)
   end