mode-matcher and sh-mode

[kevinboulain]

Hi there,

I was trying out polymode and it looks like poly-markdown has the same issue than polymode/poly-org#4.

Using

```shell
```

Will start shell-mode instead of sh-mode.

Using

```bash
```

Won't start sh-mode (so it looks like polymode-mode-name-aliases isn't applied?).

[vspinu]

Right. Something is no longer right. Will check it up.