fix wrong paths for couple of assets img -> brand

services/web/app/views/referal/bonus.jade

@@ -108,7 +108,7 @@ block content
 				method: 'feed',
 				redirect_uri: 'https://www.sharelatex.com',
 				link: '!{buildReferalUrl("fb")}',
-				picture: 'https://www.sharelatex.com/img/logo/logosmall.png',
+				picture: 'https://www.sharelatex.com/brand/logo/logosmall.png',
 				name: 'ShareLaTeX - Online LaTeX Editor',
 				caption: 'Free Unlimited Projects and Compiles',
 				description: 'ShareLaTeX is a free online LaTeX Editor. Real time collaboration like Google Docs, with Dropbox, history and auto-complete'

services/web/app/views/referal/facebookWallPost.jade

@@ -11,7 +11,7 @@ script(type='text/javascript')
           method: 'feed',
           redirect_uri: 'https://www.sharelatex.com',
           link: '#{buildReferalUrl()}',
-          picture: 'https://www.sharelatex.com/img/logo/logosmall.png',
+          picture: 'https://www.sharelatex.com/brand/logo/logosmall.png',
           name: 'ShareLaTeX - Online LaTeX Editor',
           caption: 'Free Unlimited Projects and Compiles',
           description: 'ShareLaTeX is a free Online LaTeX Editor. Real time collaboration like Google Docs, with Dropbox, history and Auto Complete'