[s2s] rougeLSum expects \n between sentences (#7410)

Co-authored-by: Swetha Mandava <smandava@nvidia.com>

examples/seq2seq/run_eval_search.py

@@ -7,13 +7,14 @@ import sys
 from collections import OrderedDict
 
 from run_eval import datetime_now, run_generate
+from utils import ROUGE_KEYS
 
 
 # A table of supported tasks and the list of scores in the order of importance to be sorted by.
 # To add a new task, simply list the score names that `run_eval.run_generate()` returns
 task_score_names = {
     "translation": ["bleu"],
-    "summarization": ["rouge1", "rouge2", "rougeL"],
+    "summarization": ROUGE_KEYS,
 }