Bump Travis CI build.
Bump Travis CI build.

rgolubtsov/nonlinear-optimization-algorithms-multilang,rgolubtsov/nonlinear-optimization-algorithms-multilang,rgolubtsov/nonlinear-optimization-algorithms-multilang,rgolubtsov/nonlinear-optimization-algorithms-multilang,rgolubtsov/nonlinear-optimization-algorithms-multilang,rgolubtsov/nonlinear-optimization-algorithms-multilang,rgolubtsov/nonlinear-optimization-algorithms-multilang