Add quotes to paths in MeCab arguments (#7142)

Without quotes directories with spaces in them will fail to be processed
correctly.

src/transformers/tokenization_bert_japanese.py

@@ -249,7 +249,7 @@ class MecabTokenizer:
                 raise ValueError("Invalid mecab_dic is specified.")
 
             mecabrc = os.path.join(dic_dir, "mecabrc")
-            mecab_option = "-d {} -r {} ".format(dic_dir, mecabrc) + mecab_option
+            mecab_option = '-d "{}" -r "{}" '.format(dic_dir, mecabrc) + mecab_option
 
         self.mecab = fugashi.GenericTagger(mecab_option)