examples/hello/print/input.md: Fix typo
examples/hello/print/input.md: Fix typo

jinyuanxie/rust-by-example-cn,jinyuanxie/rust-by-example-cn,aakloxu/rust-by-example-cn,rust-lang-cn/rust-by-example-cn,rust-lang-cn/rust-by-example-cn,aakloxu/rust-by-example-cn