cli: replace atty with std::io::IsTerminal

The `atty` crate is unmaintained[1] and `std::io::IsTerminal` was
stabilized in Rust 1.70.

[1]: https://rustsec.org/advisories/RUSTSEC-2021-0145.html

PR #2526

Cargo.lock

@@ -20,17 +20,6 @@ dependencies = [
  "memchr",
 ]
 
-[[package]]
-name = "atty"
-version = "0.2.14"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d9b39be18770d11421cdb1b9947a45dd3f37e93092cbf377614828a319d5fee8"
-dependencies = [
- "hermit-abi",
- "libc",
- "winapi",
-]
-
 [[package]]
 name = "base64"
 version = "0.20.0"
@@ -171,7 +160,6 @@ dependencies = [
 name = "grep-cli"
 version = "0.1.7"
 dependencies = [
- "atty",
  "bstr",
  "globset",
  "lazy_static",
@@ -240,15 +228,6 @@ dependencies = [
  "regex",
 ]
 
-[[package]]
-name = "hermit-abi"
-version = "0.1.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "62b467343b94ba476dcb2500d242dadbb39557df889310ac77c5d99100aaac33"
-dependencies = [
- "libc",
-]
-
 [[package]]
 name = "ignore"
 version = "0.4.20"