fix: typo error in readme

[warjiang]

the proxyConnectOptions should be corrected as proxyRequestOptions. no matter for HttpProxyAgent or HttpsProxyAgent, the agent class use proxyRequestOptions:

for HttpProxyAgent

hpagent/index.js

Lines 17 to 28 in 96f45f1

	createConnection (options, callback) {
	const requestOptions = {
	...this.proxyRequestOptions,
	method: 'CONNECT',
	host: this.proxy.hostname,
	port: this.proxy.port,
	path: `${options.host}:${options.port}`,
	setHost: false,
	headers: { ...this.proxyRequestOptions.headers, connection: this.keepAlive ? 'keep-alive' : 'close', host: `${options.host}:${options.port}` },
	agent: false,
	timeout: options.timeout || 0
	}

for HttpsProxyAgent

hpagent/index.js

Lines 74 to 86 in 96f45f1

	createConnection (options, callback) {
	const requestOptions = {
	...this.proxyRequestOptions,
	method: 'CONNECT',
	host: this.proxy.hostname,
	port: this.proxy.port,
	path: `${options.host}:${options.port}`,
	setHost: false,
	headers: { ...this.proxyRequestOptions.headers, connection: this.keepAlive ? 'keep-alive' : 'close', host: `${options.host}:${options.port}` },
	agent: false,
	timeout: options.timeout || 0
	}

[warjiang]

@delvedor could help me review that ~

[mbtools]

LGTM

[mbtools]

Duplicate of #117