elixir-lang/elixir — pull request #1951 by pragdave (2013-12-20 23:18:28+00:00)
Title: Mix warning

In the past, if the Elixir version specified by a dependency didn't match the version of Elixir used to install it, the installation was aborted. It now gives a warning instead and continues. If you see the warning, you should probably ask the writer of the dependency to verify it works with your version of Elixir and then update the requirement in their app.