travis: add astyle run for all changes in the PR
travis: add astyle run for all changes in the PR

To compare to master, use entire branch, not only files changed.

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