Lighten xed theme right-margin line to improve visibility (#714)

Author: DHager

data/xed.xml

@@ -44,7 +44,7 @@
   <style name="bracket-mismatch"            foreground="aluminium1" background="scarletred3"/>
 
   <!-- Right Margin -->
-  <style name="right-margin"                foreground="aluminium6" background="aluminium6"/>
+  <style name="right-margin"                foreground="aluminium1" background="aluminium6"/>
 
   <!-- Search Matching -->
   <style name="search-match"                background="butter1"/>