Fix tests

Composer was pulling down the latest (v2.7) of unspecified components.  This was causing mocks to fail since the API between different components wasn't matching up.
hm, lets just remove symfony 2.4 from the matrix then. its end of life anyways, now that 2.5 and 2.6 are around. and 2.3 should stay, as it is the LTS version.