Non-zero-terminated string passed to C function `puts` in smallest-hello-world.rs

[tbu-]

The title basically says it, in smallest-hello-world.rs the string "Hello!" (not zero-terminated) is passed to the C function puts which expects a zero-terminated string.

Note: Link to smallest-hello-worlds.rs goes to the offending version, for the up-to-date version, check smallest-hello-world.rs.