Correcting Yuri's Gusset Seam allowance.

As pointed out by sean#4312 in discord https://discord.com/channels/698854858052075530/757632180980547686/959311669841002566 . Yuri's grainline was indicating cut on fold whereas the seam allowance was indicating a seam. After discussing with @hellgy it was determined to be cut on fold and I was giving permission to quickly patch it. 

Changes
- Seam allowane now reflects cut on fold

Additions
- Add path.saBase to alter seam allowance correctly.

packages/yuri/src/gusset.js

@@ -38,11 +38,11 @@ export default function (part) {
     points.logo = points.title.shift(-75, 100)
     snippets.logo = new Snippet('logo', points.logo)
     if (sa) {
-      paths.sa = paths.hat
-        .offset(sa)
-        .join(paths.curve.offset(3 * sa))
-        .close()
-        .attr('class', 'fabric sa')
+	paths.saBase = new Path()
+	.move(points.right)
+	.line(points.top)
+  .setRender(false)
+	paths.sa = paths.curve.offset(3 * sa).join(paths.saBase.offset(sa)).line(points.top).close().attr('class','fabric sa')
     }
   }