fixed error for viable_models method
there are three nested levels
and the `m` in reject block is an array
which will throw `NoMethodError` for
undefined method `starts_with?' for #<Array:0x007fc424a31a98>
Merge pull request #1926 from yangchenyun/fix_viable_models_method

fixed error for viable_models method
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  fixed error for viable_models method there are three nested levels and the `m` in reject block is an array which will throw `NoMethodError` for undefined method `starts_with?' for #<Array:0x007fc424a31a98>