fix md table (#8395)

model_cards/allenai/wmt19-de-en-6-6-base/README.md

@@ -61,7 +61,7 @@ Pretrained weights were left identical to the original model released by allenai
 Here are the BLEU scores:
 
 model   |  transformers
--------|---------|----------
+-------|---------
 wmt19-de-en-6-6-base  |  38.37
 
 The score was calculated using this code:

model_cards/allenai/wmt19-de-en-6-6-big/README.md

@@ -61,7 +61,7 @@ Pretrained weights were left identical to the original model released by allenai
 Here are the BLEU scores:
 
 model   |  transformers
--------|---------|----------
+-------|---------
 wmt19-de-en-6-6-big  |  39.9
 
 The score was calculated using this code:

scripts/fsmt/gen-card-allenai-wmt19.py

@@ -85,7 +85,7 @@ Pretrained weights were left identical to the original model released by allenai
 Here are the BLEU scores:
 
 model   |  transformers
--------|---------|----------
+-------|---------
 {model_name}  |  {scores[model_name][1]}
 
 The score was calculated using this code: