Build/ESLint error output is messed up

[gaearon]

I observe this on next when I make a syntax error:

Note it's duplicated and has no color highlighting (different issue from #3790 though which got solved).

Seems like it might be caused by thread-loader in development?

If I remove thread-loader I get a different issue:

[gaearon]

I fixed the second part in 3b2c4e0.

But the first part (both duplication and lack of color) seem odd to me.

[Timer]

Fixed by #3847 and #3849.