Add Cargo.lock file from ClamAV 1.0.1 release

This change makes it so that building 1.0.2+ will not require newer
versions of the Rust compiler toolchain without us knowing about it.

This change is to support people who may be unable to use Rustup to get
the latest Rust compiler right away.

.gitignore

@@ -228,9 +228,5 @@ libclamav/c++/llvm/tools/llvmc/plugins/Base/Base.td
 debug/
 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