Updates out of date dependencies message in test.

Small failure in the following test:

      1) test warns on missing dependencies (Mix.TasksTest)
     ** (ExUnit.ExpectationError)
            expected: "Unchecked dependencies for environment dev:\n* mimetypes [git: \"git://github.com/spawngrid/mimetypes.git\"]\n  the dependency is not available, run `mix deps.get`\n* cowboy [git: \"git://github.com/extend/cowboy.git\"]\n  the dependency is not available, run `mix deps.get`\n** (Mix) Can't continue due to errors on dependencies\n"
       to match (=~): %r"Some dependencies are out of date"
     stacktrace:
       test/mix/tasks_test.exs:96: Mix.TasksTest."-test warns on missing dependencies/1-fun-0-"/0
       /Users/cloud/Projects/open-source/elixir/lib/elixir/lib/file.ex:904: File.cd!/2
       test/mix/tasks_test.exs:91: Mix.TasksTest."test warns on missing dependencies"/1

I've updated the message. Test suite passes with with https://github.com/elixir-lang/dynamo/pull/91 merged back in.

Unrelated: syntax highlight is weird in Vim for this regex, may need some investigation.