remove trailing -: the IDE2 sets it automatically

With newer versions of the IDE this was causing problems

Author: umbynos

platform.txt

@@ -133,7 +133,7 @@ pluggable_monitor.required.serial=builtin:serial-monitor
 debug.executable={build.path}/{build.project_name}.elf
 debug.toolchain=gcc
 debug.toolchain.path={runtime.tools.arm-none-eabi-gcc-7-2017q4.path}/bin/
-debug.toolchain.prefix=arm-none-eabi-
+debug.toolchain.prefix=arm-none-eabi
 debug.server=openocd
 debug.server.openocd.path={runtime.tools.openocd-0.10.0-arduino7.path}/bin/openocd
 debug.server.openocd.scripts_dir={runtime.tools.openocd-0.10.0-arduino7.path}/share/openocd/scripts/