Change URL from /blob/master/ to /blob/main/.

Author: kwwall

documentation/esapi4java-core-2.0-symmetric-crypto-user-guide.html

@@ -801,7 +801,7 @@ <H2>Acknowledgments</H2>
 KDF more in line with NIST's recommendations for KDFs as described in
 NIST Special Publication 800-108 (and specifically section 5.1). You can
 read about Jeff's review at
-<a href="https://github.com/ESAPI/esapi-java-legacy/blob/master/documentation/Analysis-of-ESAPI-2.0-KDF.pdf">
+<a href="https://github.com/ESAPI/esapi-java-legacy/blob/main/documentation/Analysis-of-ESAPI-2.0-KDF.pdf">
 Analysis of ESAPI 2.0's Key Derivation Function
 </a>
 </p>