Add shell true to windows copy

Author: Juho Hovila

mbed_flasher/flashers/FlasherMbed.py

@@ -215,7 +215,7 @@ def copy_file(self, source, destination):
     def _copy_file_windows(self, source, destination):
         command = "copy \"{}\" \"{}\"".format(os.path.abspath(source), destination)
         self.logger.debug("Copying with command: {}".format(command))
-        subprocess.check_call(command)
+        subprocess.check_call(command, shell=True)
 
     def _copy_file(self, aux_source, destination):
         destination_fd = None