Added new keyword to Ruby syntax

Signed-off-by: Mikhail S. Pobolovets <styx.mp@gmail.com>

misc/syntax/ruby.syntax

@@ -145,6 +145,7 @@ context default
     keyword whole include\? green
     keyword whole include magenta
     keyword whole require magenta
+    keyword whole require_relative magenta
 #    keyword whole where magenta
 
 #Class numeric