The *.iml file is IDE specific.  It is generated by Intellij IDEA to store project related metadata.  It is not a Play Framework specific artifact and should not be included in the PlayFramework.gitignore.

See: https://github.com/github/gitignore/pull/1581

I would also vote for the removal of .eclipse and *.eml files on similar grounds but will do so in a separate pull request.