Fix issue in imputation model

Author: nikhilwoodruff

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+    - Imputation model syntax.

policyengine_uk_data/utils/qrf.py

@@ -64,7 +64,7 @@ def predict(self, X):
         Returns:
             Predictions at the 0.5 quantile (median).
         """
-        return self.model.predict(X)[0.5]
+        return self.model.predict(X)
 
     def save(self, file_path: str):
         """