613e01afccbd4efcf002af5837897b30bb3b548a configure script: fix bug in Octave detection

================================ DYNARE MAKE CHECK MATLAB RESULTS ================================ | TOTAL: 199 | PASS: 197 | FAIL: 1 | XFAIL: 1 | XPASS: 0 | LIST OF FAILED TESTS: | * estimation/fs2000_mc6.mod

================================ DYNARE MAKE CHECK OCTAVE RESULTS ================================ | TOTAL: 197 | PASS: 196 | FAIL: 0 | XFAIL: 1 | XPASS: 0

A full log can be found on karaba in '/tmp/dynare-master-check-ttnfB0aGBY.log'.