I'm no lawyer, but I do consulting jobs for some clients with regards to DMCA takedown and online copyright enforcement. A lawyer friend had told me before that dictionary words cannot be trademarked as a "word". Think of the mess that would make. Eventually, all dictionary keywords could be trademarked, that would mean you probably can't register any domain that has an english word in it, which is utter none sense.
Trademark infringement cases are tricky, and cases of use could make a huge difference depending on intent and context. For example, Facebook cannot sue anyone having "book" in their domain name, HOWEVER, say you make a website called socialbook which is a social network that operates similarly to Facebook. Facebook can then sue claiming your domain is "confusingly similar" to their trademark and average users could misidentify the domain as affiliated with Facebook. They'd probably win that one.
Depending on how much you think using this "gig" in your domain is valuable to you, you may want to consult with a trademark lawyer first. Your other option is to do like someone else suggested and simply get the ball rolling till you get some kind of legal notice. If you do, you can choose to fight it or comply, also depending on how much value for you there is in taking both of these directions.
If your plan in anyway involves capitalizing on the Fiverr, deceiving users into thinking you're affiliated with them, then they most likely will come after you when you become big enough to be problematic. Also note that you do not really need to have bad intentions, if the way you'll use the site can be twisted by their lawyers in some way or another to make it seem like you're "capitalizing on the trademark" or being "confusingly similar" or "deceiving users" or that sort of thing, then they can still get you.
Bottom line, your alternatives:
1) Go for it and react when an action is taken against you.
2) Consult a lawyer.
3) Choose another domain.