Transformers dependency bump

Makes transformers 4.20 mandatory in the dependency lists, not because the old versions are no longer supported but because it contains fixes that benefit our users and this makes it easier for them to update to it. If you stick to an older version the OPT and XGLM workarounds we have in place will remain functional, but you miss on the enhancements newer transformers versions bring.

environments/huggingface.yml

@@ -20,4 +20,4 @@ dependencies:
     - flask-cloudflared
     - flask-ngrok
     - lupa==1.10
-    - transformers>=4.17
+    - transformers>=4.20

environments/rocm.yml

@@ -20,4 +20,4 @@ dependencies:
     - flask-cloudflared
     - flask-ngrok
     - lupa==1.10
-    - transformers>=4.17
+    - transformers>=4.20

requirements.txt

@@ -1,4 +1,4 @@
-transformers>=4.19
+transformers>=4.20
 Flask
 Flask-SocketIO
 requests