Fix crash in ESLint invocation with TIMING env set

[steelbrain]

Fixes #3045

Please see the linked issue for additional context. Here's copy-pasta of the report

In /whitespace.js a subprocess is launched to print out the rules in JSON and the JSON response is parsed.

If ESLint is being run with TIMING=1, it prints how much time each rule takes, and because the linked child process invocation is forwarding the env as-is, it's json parsing will fail and the process breaks down.