fix/sklearn_import (#530)

when ovos-classifiers was made optional this import was missed

ovos_core/intent_services/ocp_service.py

@@ -17,7 +17,6 @@
 from ovos_utils.messagebus import FakeBus
 from ovos_workshop.app import OVOSAbstractApplication
 from padacioso import IntentContainer
-from sklearn.pipeline import FeatureUnion
 
 from ovos_plugin_manager.ocp import available_extractors
 from ovos_plugin_manager.templates.pipeline import IntentMatch
@@ -1366,6 +1365,7 @@ def label2media(label: str) -> MediaType:
 
     def transform(self, X):
         if self.clf_feats:
+            from sklearn.pipeline import FeatureUnion
             vec = FeatureUnion([
                 ("kw", self.ocp_keywords),
                 ("clf", self.clf_feats)