use single quotes instead of double quotes when possible about motranslator

[zaverichintan]

In the stackoverflow answer it says that -

However the added load in doing that is so small for the last versions of PHP that most of the time the conclusion is that it doesn't really matter.
So for the performance people: use single quotes. For the "i like my code readable"-people: double quotes are a lot better for the legibility, as Flavius Stef already pointed out.

So performance boost is marginal but on the contrary $ sign changes performance. So will have to check exactly when the performance boost is effective.