Fix editor & breadcrumbs separator line color (#139)

Fixed the color of the editor & breadcrumbs separator line to use the
correct color `nord3` instead of the pinkish "test color" that should
only be used during development to quickly identify UI and syntax
elements that are affected by a specific theme color key.

Thanks to "Tom1206" again for the quick bug report.

[1]: https://github.com/Tom1206

Related to GH-125, GH-136
Fixes GH-138

resources/themes/nord.xml

@@ -61,7 +61,7 @@
     <option name="SELECTED_TEARLINE_COLOR" value="434c5e" />
     <option name="SELECTION_BACKGROUND" value="434c5e" />
     <option name="SEPARATOR_ABOVE_COLOR" value="4c566a" />
-    <option name="SEPARATOR_BELOW_COLOR" value="f000d7" />
+    <option name="SEPARATOR_BELOW_COLOR" value="4c566a" />
     <option name="SOFT_WRAP_SIGN_COLOR" value="4c566a" />
     <option name="TAB_UNDERLINE" value="88c0d0" />
     <option name="TAB_UNDERLINE_INACTIVE" value="616e88" />