examples/hello/print/README.md: fix typo
examples/hello/print/README.md: fix typo

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