Fix "Gtk: cannot open display" error on Linux

[garrettr]

Fixes #385.

Chromium's GTK frontend requires the $DISPLAY environment variable to be set. $DISPLAY is set correctly by default in a graphical session on Ubuntu 16.04, but was not being inherited by the child process spawned in util.run. Environment variables should be inherited by default according to the child_process docs, but this behavior was broken by the following recent-ish change:

brave-browser/lib/util.js

Line 20 in 7e590eb

if (!options.env) options.env = {}

@RyanJarv Can you confirm that this PR does not otherwise break the intended behavior of #229, which introduced the bug? If it does, we'll need a more sophisticated fix. Generally I think we always want to inherit the environment in subprocesses spawned by the yarn scripts, since we/Chromium use environment variables (not just $DISPLAY) for a variety of purposes.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.

Test Plan:

Same as #385 STR.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions

[RyanJarv]

Thanks for tracking this down! This was unintended and doesn't seem to affect my fix as far as I can tell, believe it was left around after a few reverts/rebases when I was working on that.

Plan to add some tests here since these scripts are pretty easy to break, will make sure to add a test for this as well.

[bbondy]

Thanks for fixing