Remove legacy linting rules

[ccnixon]

What does this PR do?
Removes the legacy linting rules and replaces them with a general rule to just flag any non-es5 syntax. This will allow us to use Standard as our code formatter while also protecting against accidentally shipping code that potentially breaks our supported browsers.

Are there breaking changes in this PR?

Has this been tested end-to-end? Please provide screenshots on how the fix now populates in the end tool. If not, what was done to test?

Any background context you want to provide?

Is there parity with the server-side/android/iOS integration (if applicable)?

Does this require a metadata change? If so, please link the PR from https://github.com/segmentio/destination-scripts.

What are the relevant tickets?

Link to CC ticket

List all the tests accounts you have used to make sure this change works

Helpful Docs

[f2prateek]

for refernce, here's how we integrated prettier into analytics.js-core segmentio/analytics.js-core#89

[ccnixon]

Thanks @f2prateek - I like that. @fathyb - from what you can tell, does the legacy eslint config help protect us more than just setting the ecmaVersion to 3?

[ccnixon]

It's tough to find compatibility tables for ie8-10

[fathyb]

@ccnixon

does the legacy eslint config help protect us more than just setting the ecmaVersion to 3?

Yes, mainly to cope with IE8 quircks:

  "rules": {
    "comma-dangle": ["error", "never"],
    "dot-notation": ["error", { "allowKeywords": false }],
    "no-catch-shadow": "error",
    "no-restricted-globals": ["error", "JSON"], // IE7
    "quote-props": ["error", "as-needed", { "keywords": true }],
    "radix": ["error", "always"]
  }

• comma-dangle prevents you from using trailing commas in object literals (which are legal per ES3 but IE8 doesn't support it)
• dot-notation will prevent you from using a keyword (ie. default) in a member expression
• no-catch-shadow prevent a bug in IE8 when a catch arguments shadows a variable in the outer scope
• no-restricted-globals to prevent using JSON (and use something like require('json') instead)
• quote-props same as dot-notation but for object literals
• radix because the behaviour of parseInt is inconsistent between ES3 and ES5

[Peripheral1994]

FWIW, we've formally deprecated support for IE8 and earlier, though I'm 👍 for continuing to informally support it if it isn't a blocker for us long-term. :)

[Peripheral1994]

e.g. We use Array.isArray in several destinations now on the clientside as a result, IIRC.

[ccnixon]

Great, thanks @fathyb!