travis-ci: fix typo in matrix
travis-ci: fix typo in matrix

Signed-off-by: Michael Heimpold <59934addbc17c0fa64a0bf4bb38537fc23439974@heimpold.de>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio