Add Cargo.lock and remove it from .gitignore for better build reproducibility

Author: sapientpants

.gitignore

@@ -97,7 +97,6 @@ target/
 
 # 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
 
 # These are backup files generated by rustfmt
 **/*.rs.bk