[ENG-3336] Darken gray notification page helper text for accessibility (

#181)

## Purpose
The helper text on the notification page was way too light, so this makes it properly contrasting with the background.

## Summary of Changes/Side Effects
1. Darkened the "To configure other…" text

## Testing Notes
Only accessibility testing needed 

## Ticket

https://openscience.atlassian.net/browse/ENG-3336

app/components/notification-list/styles.scss

@@ -25,7 +25,7 @@
 
 .helper-text {
     padding-left: 20px;
-    color: $color-text-gray-light;
+    color: $color-text-gray-dark;
 }
 
 .notification-menu {