Grammar: Add article 'the' for readability

Author: Trifall

docs/patterns/body-parser.md

@@ -15,7 +15,7 @@ head:
 ---
 
 # Body Parser
-Like Express, body-parser is a function to parse body of an incoming request.
+Like Express, body-parser is a function to parse the body of an incoming request.
 
 By default, Elysia will parse the body with content-type of:
 - `text/plain`