Allow reexporting proc macro output in the 2018 edition

Trying to use a proc macro from a 2018 edition crate in a 2018 edition crate that reexports wasm bindgen's output failed before this commit with "could not find `wasm_bindgen` in `{{root}}`".

This commit was made with 

rg " ::wasm_bindgen::" --files-with-matches | xargs sed -i 's/::wasm_bindgen::/wasm_bindgen::/g'

Author: konstin