Auto merge of #2544 - saethlin:egrep, r=saethlin

Don't use egrep, we don't need it

As of a few days ago, the latest version of `egrep` is now this:
```sh
#!/bin/sh
cmd=${0##*/}
echo "$cmd: warning: $cmd is obsolescent; using grep -E" >&2
exec grep -E "$`@"`
```
Fortunately we don't actually need ERE, so we can just drop the e.

rustup-toolchain

@@ -33,7 +33,7 @@ echo "$NEW_COMMIT" > rust-version
 shift || true # don't fail if shifting fails
 
 # Check if we already are at that commit.
-CUR_COMMIT=$(rustc +miri --version -v 2>/dev/null | egrep "^commit-hash: " | cut -d " " -f 2)
+CUR_COMMIT=$(rustc +miri --version -v 2>/dev/null | grep "^commit-hash: " | cut -d " " -f 2)
 if [[ "$CUR_COMMIT" == "$NEW_COMMIT" ]]; then
     echo "miri toolchain is already at commit $CUR_COMMIT."
     rustup override set miri