Fix treebank name typo.

scripts/train_iwpt21.py

@@ -17,7 +17,7 @@ LANG2TREEBANK = {
     "bg": ["Bulgarian-BTB"],
     "cs": ["Czech-FicTree", "Czech-CAC", "Czech-PDT", "Czech-PUD"],
     "nl": ["Dutch-Alpino", "Dutch-LassySmall"],
-    "en": ["English-EWT", "English-PUD", "UD_English-GUM"],
+    "en": ["English-EWT", "English-PUD", "English-GUM"],
     "et": ["Estonian-EDT", "Estonian-EWT"],
     "fi": ["Finnish-TDT", "Finnish-PUD"],
     "fr": ["French-Sequoia", "French-FQB"],