requirements: update to pyocd 0.15.0
requirements: update to pyocd 0.15.0

Previous release had some issues with unicode and was failing to install
in our CI. Those issues were fixed in this release.

Signed-off-by: Anas Nashif <0d9952ec84ac43c159f6b7e7ed99a9080c00dd6e@intel.com>

GiulianoFranchetto/zephyr,galak/zephyr,explora26/zephyr,ldts/zephyr,explora26/zephyr,galak/zephyr,ldts/zephyr,ldts/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,ldts/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,explora26/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr