Fix typo in wmt16

Author: Wojciech Uss

python/paddle/dataset/wmt16.py

@@ -96,7 +96,7 @@ def __get_dict_size(src_dict_size, trg_dict_size, src_lang):
     src_dict_size = min(src_dict_size, (TOTAL_EN_WORDS if src_lang == "en" else
                                         TOTAL_DE_WORDS))
     trg_dict_size = min(trg_dict_size, (TOTAL_DE_WORDS if src_lang == "en" else
-                                        TOTAL_ENG_WORDS))
+                                        TOTAL_EN_WORDS))
     return src_dict_size, trg_dict_size