Fix invalid_ember_dependencies? to actually return result

This [commit] changed return value of `run` command to be
`process.value` instead of `status`, so we need to use
`success?` now.

[commit]: ba83120

Author: krasnoukhov

lib/ember_cli/shell.rb

@@ -57,7 +57,7 @@ def test
     delegate :run, :run!, to: :runner
 
     def invalid_ember_dependencies?
-      !run("#{paths.ember} version")
+      !run("#{paths.ember} version").success?
     rescue DependencyError
       false
     end