Issue with retrieving news for multiple stocks + new news url

[sravia]

1. Latest version does not allow to retrieve news for multiple stocks ( symbols ).

Issue is in "_sanitizeCompanyNews" function.

(node:78229) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 4): AssertionError [ERR_ASSERTION]: "options.symbol" must be a non-empty string.

googleFinance.companyNews({ symbol: [ 'NASDAQ:AAPL', 'NASDAQ:MSFT' ] }, function (err, news) { }); });

2. New COMPANY_NEWS_URL is "https://finance.google.com/finance/company_news"

[pilwon]

Merged PR #20