electra config: reset the vocab size to previous default value for scope

- the vocab size was increased for proteins in commit a12354b
- as we are going to move protein related code to new repo, revert this to original value

Author: aditya0by0

configs/model/electra.yml

@@ -3,7 +3,7 @@ init_args:
   optimizer_kwargs:
     lr: 1e-3
   config:
-    vocab_size: 8500
+    vocab_size: 1400
     max_position_embeddings: 1800
     num_attention_heads: 8
     num_hidden_layers: 6