Fix the description of allow_empty arg on string_list.

* Previously the doc stated that the argument is deprecated and to use itself.

--
MOS_MIGRATED_REVID=128822795
diff --git a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
index 7256393..3e2665d 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
@@ -615,7 +615,7 @@
         name = ALLOW_EMPTY_ARG,
         type = Boolean.class,
         defaultValue = "True",
-        doc = NON_EMPTY_DOC
+        doc = ALLOW_EMPTY_DOC
       )
     },
     useAst = true,