Define DELEGATOR in targets workflow

Use DELEGATOR instead of TARGETS during the DFS for clarity

Signed-off-by: Marina Moore <mnm678@gmail.com>

Author: mnm678

tuf-spec.md

@@ -1485,8 +1485,8 @@ it in the next step.
   2. Otherwise, recursively search the list of delegations in
      order of appearance.
 
-    1. Let DELEGATEE denote the current target role TARGETS is
-       delegating to.
+    1. Let DELEGATOR be the current target role TARGETS and DELEGATEE denote
+       the current target role DELEGATOR is delegating to.
 
     2. **Download the DELEGATEE targets metadata file**, up to either
        the number of bytes specified in the snapshot metadata file, or some Z
@@ -1509,7 +1509,7 @@ it in the next step.
 
     4. **Check for an arbitrary software attack.** The new DELEGATEE
        metadata file MUST have been signed by a threshold of keys specified in the
-       TARGETS metadata file.  If the new DELEGATEE metadata file is not signed
+       DELEGATOR metadata file.  If the new DELEGATEE metadata file is not signed
        as required, abort the update cycle, and report the failure.
 
     5. **Check for a freeze attack.** The latest known time