Update app/rag_system.py: add space

app/rag_system.py

@@ -71,7 +71,7 @@ def answer_query_stream(self, query):
                     "When the user says 'you', 'your', or any pronoun, interpret it as referring to Defang with context of Defang. "
                     "If the user's question involves comparisons with or references to other services, you may use external knowledge. "
                     "However, if the question is strictly about Defang, you must ignore all external knowledge and only utilize the given context. "
-                    "Today's date is " + date.today().strftime('%B %d, %Y') + "."
+                    "Today's date is " + date.today().strftime('%B %d, %Y') + ". "
                     "Context: " + context
                 )
             }