build: specify and bump libvlc-sys version

cargo publish --dry-run
    Updating crates.io index
error: all dependencies must have a version specified when publishing.
dependency `libvlc-sys` does not specify a version

Cargo.toml

@@ -19,7 +19,7 @@ crate-type = ["rlib"]
 
 [dependencies]
 libc = "0.2"
-libvlc-sys = { path = "libvlc-sys" }
+libvlc-sys = { version = "0.2.0", path = "libvlc-sys" }
 
 [features]
 default = []