Raise a ValidationError for invalid XML

Invalid XML seems to be more of a ValidationError, not a StandardError.
Raise accordingly.

Signed-off-by: David Celis <[email protected]>

lib/onelogin/ruby-saml/logoutresponse.rb

@@ -105,7 +105,7 @@ def valid_saml?(soft = true)
         if soft
           @schema.validate(@xml).map{ return false }
         else
-          @schema.validate(@xml).map{ |error| raise(StandardError.new("#{error.message}\n\n#{@xml.to_s}")) }
+          @schema.validate(@xml).map{ |error| validation_error("#{error.message}\n\n#{@xml.to_s}") }
         end
       end
 

test/logoutresponse_test.rb

@@ -102,7 +102,7 @@ class RubySamlTest < Test::Unit::TestCase
       should "raise error for invalid xml" do
         logoutresponse = Onelogin::Saml::Logoutresponse.new(invalid_xml_response, settings)
 
-        assert_raises(StandardError) { logoutresponse.validate! }
+        assert_raises(Onelogin::Saml::ValidationError) { logoutresponse.validate! }
       end
     end