lean4 mode invalid escape char

Stream: lean4

[Zhiyuan Bao]

In lean4 mode, there are two functions'(lean4-input-compose and lean4-input-or) doc strings contain invalid escape character, which may cause this package to fail (I cannot use this package because of this reason).
I've opened a PR[1] to solve this issue, but it hasn't been merged.
I'll put the PR link here, so that somebody else who encounters this problem may find this message helpful. :blush:
[1] https://github.com/leanprover/lean4-mode/pull/38