Do proper string conversion of non-string values

Only values from the root target goes through this code, so it wasn’t causing a problem, as none of those keys had a multi-element array, but in ruby 2.0 embedding an array in a string seems to use inspect instead of to_s:

	Ruby 1.8: "#{['foo']}" #=> foo
	Ruby 2.0: "#{['foo']}" #=> ["foo"]