Command to list outdated packages

[Hurtak]

Npm currently provides npm oudated command which lists versions of currently installed packages, versions specifiend in package.json and latest avaliable version of packages.

Output of that command looks like this:

Package                    Current   Wanted   Latest  Location
babel-core                   6.7.4    6.7.4    6.9.0  project-name
babel-polyfill               6.7.4    6.7.4    6.9.0  project-name
babel-preset-es2015          6.6.0    6.6.0    6.9.0  project-name

Proposal: add elm package outdated which will show similar output to the npm outdated command

[smorele]

Good idea I think can be included in https://github.com/elm-lang/elm-package/issues/220

[rlopzc]

@Hurtak what do you think about this? https://github.com/gyzerok/elm-outdated

[Hurtak]

@romariolopezc Looks swell :)