Update lina.rnc

Added @key to lina:author

Author: dariok

rules/lina.rnc

@@ -7,7 +7,10 @@ start =
       element title { text },
       element subtitle { text }?,
       element genretitle { text }?,
-      element author { text },
+      element author { 
+        attribute key { text }?,
+        text
+      },
       element date {
       	attribute when { xsd:int }?,
       	attribute type { "print" | "premiere" | "written" }?,