Fix typo

Co-authored-by: Shane A <[email protected]>

olmo/model.py

@@ -670,7 +670,7 @@ def build(cls, layer_id: int, config: ModelConfig, cache: BufferCache) -> OLMoBl
 
 class OLMoEBlock(OLMoBlock):
     """
-    This is a a transformer MoE block where the output is computed as ``MoE(LN(x + Attention(LN(x))))``
+    This is a transformer MoE block where the output is computed as ``MoE(LN(x + Attention(LN(x))))``
     (plus another skip connection).
     """