generic-db: Improved SQLite file signature matcher to match exactly beginning of the document.

http/exposures/files/generic-db.yaml

@@ -147,10 +147,9 @@ http:
           - 200
 
       # SQLite file always starts with "SQLite format {sqlite_version}"
-      - type: word
-        part: body
-        words:
-          - "SQLite format "
+      - type: dsl
+        dsl:
+          - 'startswith(body, "SQLite format ")'
 
       # SQLite file usually contains "CREATE TABLE", meaning there is at least one table
       - type: word