Corrected format string in context.py.get_fq_identity(). (#87)

src/volttron/utils/context.py

@@ -108,7 +108,7 @@ def get_fq_identity(cls, identity, platform_instance_name=None):
         """
         if not platform_instance_name:
             platform_instance_name = cls.get_config_param("instance-name")
-        return "{platform_instance_name}.{identity}"
+        return f"{platform_instance_name}.{identity}"
 
     @classmethod
     def get_messagebus(cls):