Triangle: Update tests.

[Insti]

The common triangle test data has been updated to check properties, not types:
exercism/problem-specifications#424

The tests need to be updated to match these canonical tests.

The tests can be found in triangle_test.rb

But this would be a good time to write a generator see #396 for more information about generators.

[kotp]

Closed as referenced test generator PR is now in.