run correct test script.
run correct test script.

Travis should execute `npm run test:src` once for each version of node.
Hopefully this commit ensures that that is the case.

FSMaxB/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,josdejong/mathjs,josdejong/mathjs,josdejong/mathjs,FSMaxB/mathjs,josdejong/mathjs,josdejong/mathjs,FSMaxB/mathjs