doc: add object-curly-spacing to doc/.eslintrc

PR-URL: #13354
Refs: http://eslint.org/docs/rules/object-curly-spacing
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/.eslintrc.yaml

@@ -1,6 +1,8 @@
 ## Docs-specific linter rules
 
 rules:
+  object-curly-spacing: [2, always]
+
   # ease some restrictions in doc examples
   no-restricted-properties: 0
   no-undef: 0