update changes.txt

docs/changes.txt

@@ -46,6 +46,7 @@
 - Fixed incorrect plaintext check for 25400 and 26610. Increased plaintext check to 32 bytes to prevent false positives.
 - Fixed bug in --stdout that caused certain rules to malfunction
 - Handle signed/unsigned PDF permission P value for all PDF hash-modes
+- Fixed buffer overflow on module_26600.c / module_hash_encode()
 
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