Add temporary fix for button in Hero (#321)

Author: frankieroberto

app/assets/sass/main.scss

@@ -151,3 +151,10 @@ padding: 10px 8px;
 width: 100%;
 border-radius: 3px;
 }
+
+
+// Temporary fix until this is fixed in NHS frontend
+// See https://github.com/nhsuk/nhsuk-frontend/pull/1292
+.nhsuk-hero a.nhsuk-button {
+  color: $nhsuk-text-color;
+}