Fix typo in wasm export

[mlechon]

I'm playing with the official website example. The index.wasm example compiles, but running it in the browser produces this error:

Uncaught (in promise) CompileError: WebAssembly.instantiateStreaming(): Duplicate export name 'Clay_SetLayoutDimensions' for function 59 and function 60

It looks like a simple typo.

Love the project. Thanks!