Semicolon in location argument causes messy dstk result

Not sure if this bug needs to be prevented on the `ggmap::geocode` side, or with DSTK, but it might not hurt to design in a scrubber for semicolons (since those will force the dstk geocoder to stop and not look at the rest of the `location` argument). In this case, I think dstk is recognizing 3302 as a zip code in Czech Republic

#### Function call 1 (*WITH* semicolon) --> breaks

* geocode(location = "3302 LAVENTURE DRIVE;, Atlanta, GA", source = "dsk")
* Geocodes to"lng": 14.35, "lat": 48.7667 (Czech Republic)
* dstk url: http://www.datasciencetoolkit.org/maps/api/geocode/json?address=3302%20LAVENTURE%20DRIVE;,%20Atlanta,%20GA

#### Function call 2 (with*OUT* semicolon) --> works fine
* geocode(location = "3302 LAVENTURE DRIVE, Atlanta, GA", source = "dsk")
* Geocodes to"lng": -84.28574 , "lat": 33.88366 (Atlanta, GA)
* dstk url: http://www.datasciencetoolkit.org/maps/api/geocode/json?address=3302%20LAVENTURE%20DRIVE,%20Atlanta,%20GA