move Npm.require out of package.js

Should only be in wrench.js. This fixes the following meteor error:

wrench: updating npm dependencies -- wrench...
=> Errors prevented startup:

While building package `wrench`:
package.js:7:14: can't find npm module 'wrench'. Did you forget to call 'Npm.depends'?
Merge pull request #45 from gist-/master

move Npm.require out of package.js