Nested runs of `ie` utilize the same environment state file

To keep track of environment variables created by executing commands, we save them into a temporary file named `/tmp/env-var` after the execution of each command so that we can restore the environment variables during the execution of the next command. This means that if `ie` were to execute a doc that has a codeblock which calls `ie`, the state file will be overwritten from the nested invocation of `ie` which can break steps that come after invoking ie in a scenario.

This can be replicated with a markdown file scenario that has these 3 steps:

```bash
export VAR=foo
```

```bash
ie
```

```bash
echo $VAR # Should break because the previous command deletes the environment state.
```

This isn't a critical issue for most scenarios, but it will prevent us from having our specs execute correctly because they rely on invoking `ie` to showcase new features.