Update npm-global-without-sudo-linux.md

Updated prefix syntax for .npmrc per docs here:https://www.npmjs.org/doc/files/npmrc.html
Not sure if it is a change on the npm side, but the current syntax was creating a directory called "$HOME" instead of accessing environment vars.
Merge pull request #18 from hserang/patch-1

Update npm-global-without-sudo-linux.md