"Traveling" is the American spelling and "travelling" is the British spelling. British spelling is also used in countries such as Australia, New Zealand and Ireland. Canada generally uses British spelling, although Canadian English can be a hybrid of both American and British English. We are geographically close to the US, but historically were a British colony. As a Canadian, while I recognize both forms, I only write using British English which is typically taught in Canadian schools. However, books can be published in either British English or American English, and both spelling and vocabulary can change. Both forms are technically correct, just different.

It's a double-L in British English. They haven't broken any rules.

Traveling