Allow Cargo Lock

Modified .gitignore to allow Cargo.lock as per the recommendations
in the documentation located at:
https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html

.gitignore

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