prettier-plugin-sh Dockerfile multi-line ENV with comments doesn't \

When formatting this with `prettier-plugin-sh@0.14.0` it doesn't keep the `\` and the indenting which ends up with the Dockerfile being invalid.

```Dockerfile
# Before

ENV a=1 \
  b=2 \
  # comment
  c=3 \
  d=4 \
  # comment
  e=5
```

```Docker
# After

ENV a=1 \
  b=2
# comment
c=3 \
  d=4
# comment
e=5
```