travis: add license check for gnu library license
travis: add license check for gnu library license

mbedmicro/mbed,c1728p9/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,c1728p9/mbed-os