Fix this test failure:
1) Failure:
RelatedTagCalculatorTest#test_: A related tag calculator should convert a hash into string format.
[test/unit/related_tag_calculator_test.rb:65]:
Expected: "aaa 3 bbb 3 ccc 2 ddd 1"
Actual: "bbb 3 aaa 3 ccc 2 ddd 1"
The related tag string didn't use a stable sort. Sort first by tag
count, then by tag name.
57c4d2a54f