Added foreign key for units to entities table

migrations/2020-12-05-203809_create_units/up.sql

@@ -3,6 +3,9 @@ create table units
 (
     unit_id uuid default uuid_generate_v1() not null
         constraint untis_pk
-            primary key,
+            primary key
+        constraint units_entities_entity_id_fk
+            references entities
+            on update cascade on delete cascade,
     name text not null
 );