Set default projection dim in transformer embedder.

combo/models/embeddings.py

@@ -107,7 +107,7 @@ class TransformersWordEmbedder(token_embedders.PretrainedTransformerMismatchedEm
 
     def __init__(self,
                  model_name: str,
-                 projection_dim: int,
+                 projection_dim: int = 0,
                  projection_activation: Optional[allen_nn.Activation] = lambda x: x,
                  projection_dropout_rate: Optional[float] = 0.0,
                  freeze_transformer: bool = True,