Change category of textColor prop and correct comment

Author: Miles Hinchliffe

src/lib/components/ui/Masthead.svelte

@@ -255,7 +255,7 @@
     color: var(
       --masthead-text-color,
       #ffffff
-    ); /* Override to white for masthead */
+    ); /* Override to textColor prop if specified otherwise fall back to white */
     font-family: "GDS Transport", arial, sans-serif;
     font-weight: 700;
     font-size: 2rem;

src/wrappers/components/ui/MastheadWrapper.svelte

@@ -211,7 +211,7 @@
       },
       {
         name: "textColor",
-        category: "Content",
+        category: "Visual",
         value: "#FFFFFF",
         description: {
           markdown: true,