message: Make undercurls thickness close to underlines
  Fixes
diff: @@ -37,8 +37,9 @@ void main()
  * cos(float(x) * 2 * PI / float(cellWidth))
  + cellHeight - undercurlPosition;
  - float undercurl_top = undercurl + undercurlThickness / 2.;
  - float undercurl_bottom = undercurl - undercurlThickness / 2.;
  + // We subtract one, since curve is already 1px thick.
  + float undercurl_top = undercurl + max((undercurlThickness - 1), 0);
  + float undercurl_bottom = undercurl - max((undercurlThickness - 1), 0);
  // Compute resulted alpha based on distance from `gl_FragCoord.y` to the
  