Fix the broken build

This is really strange, as it passes on Travis for 2.3, and it passes
for me locally on 2.2. But on travis w/ 2.2, passing `Float::INFINITY`
in is resulting in an infinite loop. This should resolve it.

activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb

@@ -31,6 +31,8 @@ module ActiveRecord
 
           if value.acts_like?(:time)
             value.in_time_zone
+          elsif value.is_a?(::Float)
+            value
           else
             map(value) { |v| convert_time_to_time_zone(v) }
           end