Fix typo "gihub" in libsyntax/crateid.

Update licensing header for 2014.
auto merge of #14627 : Indiv0/rust/fix-crateid-doc-typo, r=alexcrichton

Example URL in CrateId documentation is:

    `gihub.com/mozilla/rust`

Instead of:

    `github.com/mozilla/rust`

Also update libsyntax/crateid.rs licensing header for 2014.