Fix white-space on folded lines.

butterfly/sass/_layout.sass

@@ -51,6 +51,7 @@ body
 
       .extra
         display: block
+        white-space: pre
 
   &::-webkit-scrollbar
     background: $scroll-bg

butterfly/static/main.css

@@ -2827,7 +2827,8 @@ body {
       cursor: zoom-out;
       background-color: #09080a; }
       body .line.extended.expanded .extra {
-        display: block; }
+        display: block;
+        white-space: pre; }
   body::-webkit-scrollbar {
     background: #110f13;
     width: 0.75em; }