Fix #1573 accepting dot at table names for shared tables

We have problems with geocoding of shared tables. Not sure if this will fix the whole error, but I got some 500 on console when I try to geocode a table shared to my user. The URL is this: `https://team.cartodb.com/u/juanignaciosl/api/v1/geocodings/estimation_for/marias.sample_data_for_cartodb_3` . Since [Rails routing won't allow dots by default (see 3.2)](http://guides.rubyonrails.org/v3.2.13/routing.html) `table_name` is `marias` instead of `sample_data_for_cartodb_3` (`estimation_for` will fail because `load_table` loaded nothing).