Remove Cargo.lock from the repo

[CPerezz]

The cargo.lock file should not be inside the repo. Indeed it should be added to the .gitignore file.

The .gitignore should look like:

# Generated by Cargo
# will have compiled files and executables
/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