Fix typo in platform= documentation
Merge pull request #1048 from jasonrclark/fix_platform_typo

Fix typo in platform= documentation [ci skip]
Add #1048 to History start RG version 2.5 section
Drop `rescue TSort::Cyclic` from `Gem::{DependencyList,RequestSet}#tsort_each_child`.

`TSort::Cyclic` is only raised from `TSort.tsort_each`, not from `TSort#strongly_connected_components` which is used here. Even then, the exception is raised outside the child iterator and thus cannot be rescued in `#tsort_each_child`.

Originally introduced in f554bc5 and a1d35cd, respectively.