[Doppins] Upgrade dependency superagent to ^2.3.0

[doppins-bot]

Hi!

A new version was just released of superagent, so Doppins
has upgraded your project's dependency ranges.

Make sure that it doesn't break anything, and happy merging!

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Upgraded superagent from ^1.2.0 to ^2.1.0

Changelog:

Version 2.0.0

Breaking changes

Breaking changes are in rarely used functionality, so we hope upgrade will be smooth for most users.

• Browser: The .parse() method has been renamed to .serialize() to avoid inconsistency with NodeJS version (v1.8.3 supports .serialize() too)
• Browser: Query string keys without a value used to be parsed as 'undefined', now their value is '' (empty string) (shura, Kornel Lesiński).
• NodeJS: The redirect event is called after new query string and headers have been set and is allowed to override the request URL (Kornel Lesiński)
• .then() returns a real Promise. Note that use of superagent with promises now requires a global Promise object.
  If you target Internet Explorer or Node 0.10, you'll need require('es6-promise').polyfill() or similar.
• Upgraded all dependencies (Peter Lyons)
• Renamed properties documented as ``@api privateto have`_prefixed` names (Kornel Lesiński)

Probably not breaking changes:

• Extracted common functions to request-base (Peter Lyons)
• Fixed race condition in pipe tests (Peter Lyons)
• Handle FormData error events (scriptype)
• Fixed wrong jsdoc of Request#attach (George Chung)
• Updated and improved tests (Peter Lyons)

Version 2.1.0

• Wait for async parsers to avoid double callback (Kornel Lesiński)
• DRY parser selection and response creation code (Kornel Lesiński)
• Treat multipart like other parsers (Kornel Lesiński)
• Errors thrown in .end() callback don't cause the callback to be called twice (Kornel Lesiński)

Version 2.0.0

[doppins-bot]

An additional new version was just released of superagent, so we've added an
extra commit upgrading your range to ^2.2.0.

Hope that's alright!
— Doppins

[doppins-bot]

An additional new version was just released of superagent, so we've added an
extra commit upgrading your range to ^2.3.0.

Hope that's alright!
— Doppins