ignore_case option for get_best_sense and get_other_senses does not check for lowercase

[chanind]

The ignore_case option for get_base_sense and get_other_senses claims that: "ignore_case (bool): Check for uppercase, lowercase and titlecase." However, ignore_case does not check for lowercase - it only checks for the version of the word passed in, upper-case, and title-case (https://github.com/explosion/sense2vec/blob/master/sense2vec/sense2vec.py#L250). It should also lower-case the word so that it correctly ignores case.