[hotfix] Fix typo in error message

This closes #104
diff --git a/statefun-python-sdk/statefun/core.py b/statefun-python-sdk/statefun/core.py
index 50c1492..8f6e856 100644
--- a/statefun-python-sdk/statefun/core.py
+++ b/statefun-python-sdk/statefun/core.py
@@ -224,7 +224,7 @@
     if not value:
         raise ValueError("Missing value")
     if not partition_key:
-        raise ValueError("Missung partition key")
+        raise ValueError("Missing partition key")
     record = KinesisEgressRecord()
     record.stream = stream
     record.value_bytes = value.SerializeToString()