fix possible windows bossac tool

Author: hathach

platform.txt

@@ -143,6 +143,7 @@ tools.bossac.upload.network_pattern="{network_cmd}" -address {serial.port} -port
 
 tools.bossac18.path={runtime.tools.bossac-1.8.0-48-gb176eee.path}
 tools.bossac18.cmd=bossac
+tools.bossac18.cmd.windows=bossac.exe
 
 tools.bossac18.upload.params.verbose=-i -d
 tools.bossac18.upload.params.quiet=