Build failures in Nightly due to Proc macro API 1.2

[tirkarthi]

Project fails with Nightly compiler due to the recent proc macro API changes made that renames some of the components. It seems the release of proc macros 2 library with the changes already released which will fix the issue. I searched for issues here and couldn't find anything related to this. Hence I am opening this as a reminder. Feel free to close this if it's tracked elsewhere or irrelevant due to semver in cargo.toml using the latest version.

Upstream rustc issue reference : rust-lang/rust#50473 (comment)
Upstream proc macros 2 PR (merged) : dtolnay/proc-macro2#90
0.4.3 release : https://github.com/alexcrichton/proc-macro2/tree/0.4.3

Thanks

[alexcrichton]

Fixed in e76f553!