Update summary.en.md

Author: alisolphp

books/Enterprise Integration Patterns/summary.en.md

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 # Book Summary: Enterprise Integration Patterns
 * **Author**: Gregor Hohpe, Bobby Woolf
 * **Genre**: Software Engineering
-* **Publication Date**: October 10, 2003
+* **Publication Date**: 2003
 * **Book Link**: https://amazon.com/dp/0321200683
 
 This document summarizes the key lessons and insights extracted from the book.