Set exit code when commands fail

If I run git node land on a new machine with nothing configured, I'll get the instructions to set required variables, and then the process will exit with status code 0. In order for us to be able to use ncu on a Commit Queue, it needs to return the appropriate status codes when something goes wrong, otherwise automation won't work.

(I didn't check which other failures will exit with 0, but all failures should set the exit code to a non-zero code)

首先在未设置所需变量的新机器上复现 git node land，然后跟踪失败是如何退出的。检查报告错误的 ncu 命令路径；当失败返回非零状态码，使 Commit Queue 自动化能够检测到它们时，即表示完成。