fix(grid)grid: makes offsets for s1 and s2 consistent with l and m

Offsets for 's' were not consistent with 'l' and 'm' causing unexpected behaviour. Now they all work the same

Fixes: #657

Author: svalo

sass/_grid.scss

@@ -65,8 +65,8 @@ body {
   .s11 { grid-column: auto / span 11; }
   .s12 { grid-column: auto / span 12; }
 
-  .offset-s1 { grid-column-start:  3; }
-  .offset-s2 { grid-column-start:  2; }
+  .offset-s1 { grid-column-start:  2; }
+  .offset-s2 { grid-column-start:  3; }
   .offset-s3 { grid-column-start:  4; }
   .offset-s4 { grid-column-start:  5; }
   .offset-s5 { grid-column-start:  6; }