[BUG] Building Cursive with `--features ansi` yields a future incompatibility warning due to nom v4.2.3

**Describe the bug**
Not a bug, but a compiler warning. Cursive built with ansi will print a warning that it will not build in a future version of Rust.

```
warning: the following packages contain code that will be rejected by a future version of Rust: nom v4.2.3
```

The slightly more detailed report suggests to upgrade to a newer version of nom.

**To Reproduce**

```
cargo build --features ansi
...
warning: the following packages contain code that will be rejected by a future version of Rust: nom v4.2.3
```

**Expected behavior**
I would hope the latest version of Cursive would build on future versions of Rust.

**Environment**

macOS 13.5

```
uname -v
Darwin Kernel Version 22.6.0: Wed Jul 5 22:22:05 PDT 2023; root:xnu-8796.141.3~6/RELEASE_ARM64_T6000

cargo --version
cargo 1.70.0 (ec8a8a0ca 2023-04-25)

rustc --version
rustc 1.70.0 (90c541806 2023-05-31)
```