HackerNews: Change the tab name from "News" to "Social"

Since reddit is using "Social", HN should probably use it too. I don't particularly like the tab name "News" because it implies that the results that I get are timely (and HN does not necessarily have timely stuff).
Merge pull request #768 from duckduckgo/jag/hackernews

HackerNews: Change the tab name from "News" to "Social"