`cargo install cargo-src` fails on nightly

[Berkus Decker]

error[E0603]: struct `ParseSess` is private
  --> /Users/berkus/.cargo/registry/src/github.com-1ecc6299db9ec823/rustdoc-highlight-0.1.9/src/lib.rs:54:23
   |
54 |     let sess = parse::ParseSess::new(FilePathMapping::empty());
   |                       ^^^^^^^^^

error[E0603]: struct `ParseSess` is private
  --> /Users/berkus/.cargo/registry/src/github.com-1ecc6299db9ec823/rustdoc-highlight-0.1.9/src/lib.rs:93:23
   |
93 |     let sess = parse::ParseSess::new(FilePathMapping::empty());
   |                       ^^^^^^^^^

   Compiling rls-span v0.4.1
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0603`.
error: Could not compile `rustdoc-highlight`.

rustc --version:
rustc 1.40.0-nightly (87cbf0a54 2019-11-01)
cargo --version:
cargo 1.38.0

[Nick Cameron]

Hi, this should be fixed now. Thanks for the bug report!