Fix grammar in en/try_ruby_390.md (#58)
Fix grammar in en/try_ruby_390.md (#58)

* `Its` is a possessive form of the pronoun `it`, meaning belonging to it.
* `It's` is a contraction of the words `it is` or `it has`.
easydatawarehousing/TryRuby,easydatawarehousing/TryRuby,easydatawarehousing/TryRuby