message: fix(readme): remove uneeded feature flag
diff: @@ -68,7 +68,7 @@ check out our [contribution policy].
  3. Add this to the top of your `src/lib.rs`:
  ```rust
  - #![feature(use_extern_macros, wasm_import_module)]
  + #![feature(use_extern_macros)]
  extern crate wasm_bindgen;
  