ANSI escape sequences to display colored output not handled correctly

I experienced this bug when trying to run the [QuickJS wasm] file. I have created a repo to reproduce the issue.

- What are the steps to reproduce the issue?
1. Clone https://github.com/samrat/wasmtime-colored-output
2. Build the wasm file: `cargo build --target wasm32-wasi`
3. Run the file with wasmtime: `wasmtime target/wasm32-wasi/debug/wasmtime-colored-output.wasm`

- What do you expect to happen? What does actually happen? Does it panic, and
if so, with which assertion?
I expected to see colored output, the ASCII escape codes are displayed instead.

- Which Wasmtime version / commit hash / branch are you using?
`c202a8eea`

- If relevant, can you include some extra information about your environment?
(Rust version, operating system, architecture...)
```
rustc 1.43.0-nightly (564758c4c 2020-03-08)

> uname -r
5.5.9-arch1-2
```