Add the semicolon missing from the generated main.rs contents.

When you run `cargo new project-name --bin`, a project is generated by cargo
with a file, `src/main.rs`. This file has a main function with one line that
prints hello, world, but a semicolon is missing from the end of the
expression.
auto merge of #845 : jbranchaud/cargo/add-missing-semicolon-for-new-project-main, r=alexcrichton

When you run `cargo new project-name --bin`, a project is generated by cargo
with a file, `src/main.rs`. This file has a main function with one line that
prints hello, world, but a semicolon is missing from the end of the
expression.