Fix for using lists() and key formatted like 'table.field'

Sorry this thing isn't pretty.

This fixes an error where you wouldn't be able to use the lists function if your query had joins.

Heres the code I was running that caused me errors.

Question::join('question_survey', 'questions.id', '=', 'question_survey.question_id')
						->where('question_survey.survey_id', $surveyId)
						->join('tags', 'questions.tag_id', '=', 'tags.id')
						->where('tags.category_id', $categoryId)
						->lists('questions.id');

Signed-off-by: Andreas Heiberg <git@andreas-heiberg.com>