Set the lang env by using os-locale

[Stanzilla]

This is #605 rebased and @leo's comment addressed.

I tested that it still works correctly on en_US

[albinekb]

I think this is ready to merge, we had LGTM in the old PR, same code just the dep added.

[chabou]

Works great
Before:

After:

[pi0]

This is causing warns when my locale is not en_US:

MacOS Mojave 10.14.2 (18C54) / Hyper 2.1.0 stable

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LC_ALL = (unset),
        LC_CTYPE = "en_IR.UTF-8",
        LANG = "en_IR.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LC_ALL = (unset),
        LC_CTYPE = "en_IR.UTF-8",
        LANG = "en_IR.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

The current workaround is manually set env in ~/.hyper.js:

{
    env: {
     LANGUAGE: 'en_US.UTF-8',
     LC_ALL: 'en_US.UTF-8',
     LANG: 'en_US.UTF-8',
     LC_TYPE: 'en_US.UTF-8',
    },
}

[pi0]

More investigations: os-locale will use defaults read -g AppleLocale command to compute locale which resolves to en_IR which is an invalid (at least perl) locale. We may need a validation mecanism over it.