Replace dependency CircularJSON with its successor flatted

[cclauss]

Every time our Travis CI tests run, they generate the following warning:
$ npm install

npm WARN deprecated circular-json@0.3.3: CircularJSON is in maintenance only, flatted is its successor.

Would it be worthwhile to make this switch from the deprecated CircularJSON --> flatted?
Both are from WebReflection but they do NOT share the same LICENSE.

• Node Version:
• Platform:
• Compiler:
• Module:

Verbose output (from npm or node-gyp):

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[bnoordhuis]

That's not under our control. It's not a direct dependency, not even close:

$ npm ls circular-json
node-gyp@5.0.3 /Users/bnoordhuis/src/node-gyp
└─┬ standard@12.0.1
  └─┬ eslint@5.4.0
    └─┬ file-entry-cache@2.0.0
      └─┬ flat-cache@1.3.4
        └── circular-json@0.3.3 

[rvagg]

needs an upgrade to standard@13

However there's a new rule for no spacing inside square brackets that makes my blood boil: standard/standard#1318

Let me get over my syntax rage and I'll put in a PR to "fix" this.