chore: correct cross metadata key in Cargo.toml. (#30)

As `sprocket` is not in a workspace, it should be using the package metadata
key.

Author: peterhuene

Cargo.toml

@@ -29,7 +29,7 @@ indicatif = "0.17.8"
 clap-verbosity-flag = "2.2.1"
 
 # Install openssl for the linux arm64 build
-[workspace.metadata.cross.target.aarch64-unknown-linux-gnu]
+[package.metadata.cross.target.aarch64-unknown-linux-gnu]
 pre-build = [
     "dpkg --add-architecture $CROSS_DEB_ARCH",
     "apt-get update && apt-get --assume-yes install libssl-dev:$CROSS_DEB_ARCH"