Update travis: Remove 5.2 and set 5.3 to precise
Update travis: Remove 5.2 and set 5.3 to precise

Now support for both 5.1 and 5.2 are *not* CI tested, and will
not be frequently manually tested. Bugs in 5.1/5.2 will be
fixed on an as-discovered basis, which in the past has proven
to be very infrequently indeed.

jnvsor/kint,michabbb-backup/kint,jnvsor/kint,kint-php/kint,michabbb-backup/kint,kint-php/kint