Fix user agent header and include node.js version

[gurpreetatwal]

Fixes the user-agent header so that it reports the version of the client making the request as opposed to Smartcar API being accessed (which is in the URL) as it currently does.

I also added in the version of node.js that the request was made from for tracking of which node version we should support. Please take a close look at the format of the header as well as if we should be including more or less information in it. (first glance process.platform might be useful for windows/osx/linux support)

Format: smartcar-node-sdk:<pkg-version> (node.js <node-version>) Example: smartcar-node-sdk:3.0.2 (node.js v6.14.3)

Examples of headers from other API libraries:

• Sendgrid: sendgrid/<pkg-version>;nodejs
• Twillio : twilio-node/<pkg-version> (node.js <node-version>)
• Plaid: Plaid Node v<pkg-version>
• Lob: Lob/v1 NodeBindings/<pkg-version>
• PayPal: PayPalSDK/PayPal-node-SDK <pkg-version> (node <node-version>-${process.arch}-${process.platform}; OpenSSL ${process.versions.openssl}
• AWS: aws-sdk-nodejs/<pkg-version> ${process.platform}/<node-version>
• Stripe:

  JSON.stringify({
  bindings_version: Stripe.PACKAGE_VERSION,
  lang: 'node',
  lang_version: process.version,
  platform: process.platform,
  publisher: 'stripe',
  uname: <output of `uname -a`>
  })

[KarthikBhaskara]

@gurpreetatwal Any reason why we're choosing to use : instead of /. Seems like other api's are using /. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent#Syntax

[gurpreetatwal]

Thoughts on:

`Smartcar/${pkg.version} (${process.platform}; ${process.arch}) Node.js ${process.version} `
'Smartcar/4.0.1 (Linux; x64) Node.js 6.14.3'

[sankethkatta]

/^Smartcar\/(\d+\.\d+\.\d+) \((\w+); (\w+)\) Node.js (\d+\.\d+\.\d+)$/

[gurpreetatwal]

/^Smartcar\/(\d+\.\d+\.\d+-[\w-]*) \((\w+); (\w+)\) Node.js (v\d+\.\d+\.\d+)$/

need to include any specifiers after version like 3.0.0-rc1

[sankethkatta]

@gurpreetatwal do you need the specifiers for the process version as well?

[emrebsonmez]

lgtm, just address @sankethkatta's remarks :rocket:

[emrebsonmez]

mr. realtime ;)

[gurpreetatwal]

@sankethkatta at least for Node, I don't think so