GUACAMOLE-773: Update Java dependencies to latest stable, compatible versions.

doc/licenses/spring-security-5.6.1/NOTICE

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+This product includes software developed by Spring Security
+Project (https://www.springframework.org/security).

doc/licenses/spring-security-5.6.1/README

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+Spring Security (https://spring.io/projects/spring-security)
+------------------------------------------------------------
+
+    Version: 5.6.1
+    From: 'Spring' (https://spring.io/)
+    License(s):
+        Apache v2.0
+

doc/licenses/spring-security-5.6.1/dep-coordinates.txt

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+org.springframework.security:spring-security-core:jar:5.6.1
+org.springframework.security:spring-security-crypto:jar:5.6.1
+org.springframework.security:spring-security-web:jar:5.6.1