Fixing bug in REGEX validating MODEL_ID

There was an error in the part of the regex that validates model_id for
shared models.
Fixes an issue in local models when predicting with text fields

If the term to predict with contains special regex chars (*?$ ...) there
was an exception in the `Pattern.compile`
Merge pull request #13 from osroca/master

Fixes bug in local predictions reported by a BigML user

There are a couple of broken tests testing with spam.csv due to the new Source server config that makes that the field "Text" is taken as categorical instead of text. I'll fix them asap.