update shortcut for go-to-line

regarding go-to-line - http://www.emacswiki.org/emacs/GotoLine
about "recentering" - I was unable to get it working on my emacs24 (ubuntu, fresh installation). Manual describes a bit different shortcuts: https://www.gnu.org/software/emacs/manual/html_node/emacs/Recentering.html
Merge pull request #13 from psihonavt/patch-2

update shortcut for go-to-line