Disregard order of HashMap entries in unit tests

FormDataTableTest *transforms_to_map_of_double_to_double* should not rely on [Map#toString()](http://docs.oracle.com/javase/7/docs/api/java/util/AbstractMap.html#toString()) to test values in a Map, which relies on the order of the Map's EntrySet iterator. In the case of HashMaps, used by cucumber, that order is unpredictable, and (can be) different in Java8 from previous versions, causing tests to fail.

This patch tests the mapping directly, and disregards iteration order.