Track Cargo.lock in Git (webrtc-rs#503)

* Track `Cargo.lock` in Git

* Fix clippy warnings

Author: thomaseizinger

.gitignore

@@ -5,11 +5,6 @@
 /crates/target/
 /crates/.idea/
 
-# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
-# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
-/crates/Cargo.lock
-
 # These are backup files generated by rustfmt
 **/*.rs.bk