Perfectly center mastodon logo on mobile landing page (#4339)

Setting only padding-left made the logo left-shifted on mobile page. Margin-right was old setting for adjusting clearance between old logo and letter "Mastodon".

app/javascript/styles/about.scss

@@ -455,12 +455,12 @@
       .brand {
         a {
           padding-left: 0;
+          padding-right: 0;
           color: $white;
         }
 
         img {
           height: 32px;
-          margin-right: 10px;
           position: relative;
           top: 4px;
           left: -10px;
@@ -728,7 +728,6 @@
       .links .brand img {
         left: 0;
         top: 0;
-        margin-right: 0;
       }
 
       .hero {