tools: enable rest-spread-spacing

There are currently 17 instances of the spread operator and all of them
have no space between the operator and the subsequent argument. This
change enables a lint rule to enforce that same style on any future uses
of the spread operator.

Refs: https://github.com/nodejs/node/pull/6573/files/7a1b47f329f2e6481ef8f54951570197fd98378d#r74479351
PR-URL: #8073
Reviewed-By: cjihrig - Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: targos - Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>

.eslintrc

@@ -87,6 +87,7 @@ rules:
   no-new-symbol: 2
   no-this-before-super: 2
   prefer-const: 2
+  rest-spread-spacing: 2
   template-curly-spacing: 2
 
   # Custom rules in tools/eslint-rules