fix: pass proxy credentials to binary download (fixes #164)

[Arunendra21]

What

browserstack-local-nodejs already accepts proxyUser / proxyPass and forwards them to the BrowserStackLocal binary as --proxy-user / --proxy-pass (see Local.js). However, when the library downloads the binary itself, LocalBinary.download() builds the HttpsProxyAgent with only host and port:

options.agent = new HttpsProxyAgent({
  host: conf.proxyHost,
  port: conf.proxyPort
});

So behind a proxy that requires authentication, the binary download fails with 407 Proxy Authentication Required even when the user has supplied valid proxy credentials. This is #164.

Fix

Include the credentials in the proxy agent options when both proxyUser and proxyPass are provided. https-proxy-agent@^5 (the version already used here) accepts an auth: "user:pass" option, which it sends as the Proxy-Authorization header:

var proxyOptions = { host: conf.proxyHost, port: conf.proxyPort };
if (conf.proxyUser && conf.proxyPass) {
  proxyOptions.auth = conf.proxyUser + ':' + conf.proxyPass;
}
options.agent = new HttpsProxyAgent(proxyOptions);

The change is scoped to the download path and only adds auth when both credentials are present, so existing unauthenticated-proxy and no-proxy behaviour is unchanged.

Tests

Added two tests to test/local.js (they stub https.get, so no network is required):

• credentials present -> the proxy agent carries auth: "user:pass".
• only host/port -> no auth is set (behaviour unchanged).

Fixes #164