add smart `env` command if there is none present

adding a "env":"env" run-script to my package every time i want to double check some environment var, and then removing to commit my changes, always feel awkward... but now that is a thing of the past! People from the future will be able to look at kids, raise their trembling canes, and say that in their time they had to add a 'env' rule to check their environment variables and that kids have it too easy today. I can't wait to have it too easy.

this little patch adds the ability to run `npm env` even if there is no such rule added to the package. and it also works across all platforms. (caveat, only tested on linux and windows7, but osx and others should also work with the linux rule)

PS: also removed a few `;` from the original code to conform to style guide.