Fix up build warnings about use of []

[bossmc]

Simple PR to fix some build warnings on a clean clone of master.

/home/ubuntu/src/rust/src/librustc/middle/astconv_util.rs:71:51: 71:53 warning: obsolete syntax: []
/home/ubuntu/src/rust/src/librustc/middle/astconv_util.rs:71 Some(prim_ty_to_ty(tcx, &path.segments[], nty))
^~
note: write `[..]` instead
...
/home/ubuntu/src/rust/src/librustc_resolve/lib.rs:2988:53: 2988:55 warning: obsolete syntax: []
/home/ubuntu/src/rust/src/librustc_resolve/lib.rs:2988 self.resolve_error(trait_path.span, &msg[]);
^~
note: write `[..]` instead

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @huonw (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[alexcrichton]

@bors: r+ d9bdc43 rollup

[alexcrichton]

Thanks!

[Manishearth]

This is superseded by #22835, I think.

[bossmc]

@Manishearth Agreed (though that PR's changes are slightly different in a few places). I'm happy for this to be closed if that change is merged.

[bors]

☔ The latest upstream changes (presumably #22860) made this pull request unmergeable. Please resolve the merge conflicts.