Show UTC timestamp in Time diffs when zone differs

This should help some people even more quickly see why the two dates are
different moments in time as they won't have to do the offset
calculation in their heads when they see the difference in hours/minutes
and gmt_offset.

Author: Mange

lib/super_diff/operational_sequencers/time_like.rb

@@ -14,7 +14,16 @@ def self.applies_to?(expected, actual)
       protected
 
       def attribute_names
-        ["year", "month", "day", "hour", "min", "sec", "nsec", "zone", "gmt_offset"]
+        base = ["year", "month", "day", "hour", "min", "sec", "nsec", "zone", "gmt_offset"]
+
+        # If timezones are different, also show a normalized timestamp at the
+        # end of the diff to help visualize why they are different moments in
+        # time.
+        if actual.zone != expected.zone
+          base + ["utc"]
+        else
+          base
+        end
       end
     end
   end

spec/integration/rspec/eq_matcher_spec.rb

@@ -290,8 +290,10 @@
             plain_line "    nsec: 0,"
             alpha_line "-   zone: \"CET\","
             beta_line  "+   zone: \"UTC\","
-            alpha_line "-   gmt_offset: 3600"
-            beta_line  "+   gmt_offset: 0"
+            alpha_line "-   gmt_offset: 3600,"
+            beta_line  "+   gmt_offset: 0,"
+            alpha_line "-   utc: 2011-12-13 15:15:16.000 UTC +00:00 (Time)"
+            beta_line  "+   utc: 2011-12-13 14:15:16.000 UTC +00:00 (Time)"
             plain_line "  }>"
           },
         )