WASM compilation error

[dr-orlovsky]

On all platforms except UNIX and Windows (for instance with cargo build --target wasm32-unknown-unknown):

   Compiling compiletest_rs v0.11.0
error[E0596]: cannot borrow `out_pipe` as mutable, as it is not declared as mutable
  --> /Users/orlovsky/.cargo/registry/src/index.crates.io-6f17d22bba15001f/compiletest_rs-0.11.0/src/read2.rs:27:9
   |
27 |         out_pipe.read_to_end(&mut buffer)?;
   |         ^^^^^^^^ cannot borrow as mutable
   |
help: consider changing this to be mutable
   |
22 |         mut out_pipe: ChildStdout,
   |         +++

error[E0596]: cannot borrow `err_pipe` as mutable, as it is not declared as mutable
  --> /Users/orlovsky/.cargo/registry/src/index.crates.io-6f17d22bba15001f/compiletest_rs-0.11.0/src/read2.rs:30:9
   |
30 |         err_pipe.read_to_end(&mut buffer)?;
   |         ^^^^^^^^ cannot borrow as mutable
   |
help: consider changing this to be mutable
   |
23 |         mut err_pipe: ChildStderr,
   |         +++

error: aborting due to 2 previous errors