Made pre-commit work in sillicon macos and linux

While running the previous version of the precommit I got the following
error:
```
Found configured hook: pre-commit
Running command: sh pre-commit
Fetching advisory database from
  `https://github.com/RustSec/advisory-db.git`
Updating crates.io index
Scanning Cargo.lock for vulnerabilities (184 crate dependencies)
src/jailer/src/env.rs
sed: illegal option -- z
usage: sed script [-Ealnru] [-i extension] [file ...]
sed [-Ealnu] [-i extension] [-e script] ... [-f script_file]
  ... [file ...]
Configured hook command failed
pre-commit hook rejected
```

Tested a couple different things and the `paste` command seemed to work
both on macos (M1) and on linux (tested it in an ubuntu:22.04
container).

Signed-off-by: seafoodfry <[email protected]>

Author: seafoodfry

Diff for: pre-commit

@@ -23,7 +23,7 @@ for i in $(git diff --name-only --cached --diff-filter=d); do
     extension="${filename##*.}"
     if [ "$extension" = "rs" ]; then
         # Read rustfmt config, replace '\n' with ','
-        rustfmt_config="$(sed -z "s/\n/,/g;s/,$/\n/" ./tests/fmt.toml)"
+        rustfmt_config="$(paste -sd, ./tests/fmt.toml)"
         # We first do a check run, this will fail when it finds a non-matching license.
         rustfmt $i --check --config $rustfmt_config
         # Run `cargo fmt` for this file