chore(deps): update superagent requirement from ^4.1.0 to ^5.1.0

[dependabot-preview]

Updates the requirements on superagent to permit the latest version.

Release notes

Sourced from superagent's releases.

v5.1.0

• Disable setting default user-agent (#1495) e652b8c

forwardemail/superagent@v5.0.9...v5.1.0

Changelog

Sourced from superagent's changelog.

4.1.0 (2018-12-26)

• .connect() IP/DNS override option (Kornel)
• .trustLocalhost() option for allowing broken HTTPS on localhost
• .abort() used with promises rejects the promise.

4.0.0 (2018-11-17)

Breaking changes

• Node.js v4 has reached it's end of life, so we no longer support it. It's v6+ or later. We recommend Node.js 10.
• We now use ES6 in the browser code, too.
  • If you're using Browserify or Webpack to package code for Internet Explorer, you will also have to use Babel.
  • The pre-built node_modules/superagent.js is still ES5-compatible.
• .end(…) returns undefined instead of the request. If you need the request object after calling .end() (and you probably don't), save it in a variable and call request.end(…). Consider not using .end() at all, and migrating to promises by calling .then() instead.
• In Node, responses with unknown MIME type are buffered by default. To get old behavior, if you use custom unbuffered parsers, add .buffer(false) to requests or set superagent.buffer[yourMimeType] = false.
• Invalid uses of .pipe() throw.

Minor changes

• Throw if req.abort().end() is called
• Throw if using unsupported mix of send and field
• Reject .end() promise on all error events (Kornel Lesiński)
• Set https.servername from the Host header (Kornel Lesiński)
• Leave backticks unencoded in query strings where possible (Ethan Resnick)
• Update node-mime to 2.x (Alexey Kucherenko)
• Allow default buffer settings based on response-type (shrey)
• response.buffered is more accurate.

3.8.3 (2018-04-29)

• Add flags for 201 & 422 responses (Nikhil Fadnis)
• Emit progress event while uploading Node Buffer via send method (Sergey Akhalkov)
• Fixed setting correct cookies for redirects (Damien Clark)
• Replace .catch with ['catch'] for IE9 Support (Miguel Stevens)

3.8.2 (2017-12-09)

• Fixed handling of exceptions thrown from callbacks
• Stricter matching of +json MIME types.

3.8.1 (2017-11-08)

• Clear authorization header on cross-domain redirect

3.8.0

• Added support for "globally" defined headers and event handlers via superagent.agent(). It now remembers default settings for all its requests.
• Added optional callback to .retry() (Alexander Murphy)

... (truncated)

Commits

• 977f0ad v5.1.0
• e652b8c Disable setting default user-agent (#1495)
• 483f816 v5.0.9
• 2e5d6fd feat: added fast-safe-stringify instead of JSON.stringify (closes #1464)
• 6dc3eaa v5.0.8
• 28e7101 fix: removed @babel/transform-runtime (closes #1494)
• 974ac02 v5.0.7
• a44cca8 fix: switch browserify to use babelify as global transform, bump deps
• 0a822ab docs: fixed arrow function for example
• 4dd96c0 v5.0.6
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #4221.