tools: enable ES2016 support in ESLint
Checklist
-
make -j8 test
(UNIX), orvcbuild test nosign
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
tools
Description of change
This allows to use the exponentiation operator.
Ref: https://github.com/nodejs/node/pull/9208#issuecomment-255309920