99ca97919019345aab3eec5282ee92ad11b8fdfe build: texi2dvi on os x is too old, modify build instructions accordingly

================================ DYNARE MAKE CHECK MATLAB RESULTS ================================ | TOTAL: 433 | PASS: 431 | FAIL: 0 | XFAIL: 2 | XPASS: 0

================================ DYNARE MAKE CHECK OCTAVE RESULTS ================================ | TOTAL: 431 | PASS: 429 | FAIL: 0 | XFAIL: 2 | XPASS: 0

A full log can be found on karaba in '/tmp/dynare-master-check-pGqKCf2orS.log'.