message: fix(docs): remove duplicated "is"
diff: @@ -15,7 +15,7 @@ responsive.
  [An analysis](http://fitzgeraldnick.com/2018/02/09/wee-alloc.html) suggests that over half of the bare minimum WebAssembly memory footprint is required by Rust's default memory allocator. Yet, WebAssembly code often does not require a sophisticated allocator, since it often just requests a couple of large initial allocations.
  `wee_alloc` trades off size for speed. It has a tiny code-size
  -footprint, but it is is not competitive in terms of performance with the
  +footprint, but it is not competitive in terms of performance with the
  default global allocator, for example.
  For even more details, see the [`wee_alloc`
  