Get Browser DOM example working

[happybeing]

An example which adds a paragraph to the web page using DOM bindings from https://github.com/ibaryshnikov/rust-workshop-21-dec-2018 is not yet working. It's probably a simple fix but I don't have the time to dig into this at the moment, so a solution or PR would be welcome. It's just one Rust function here:

https://github.com/happybeing/svelte-wasi-with-rust/blob/main/src/rust-wasi-example/src/main.rs#L72-L84