Upgrade to Spring Framework 5.3.26.

Closes gh-771

Author: mp911de

pom.xml

@@ -27,7 +27,7 @@
 		<kotlin-coroutines.version>1.4.3</kotlin-coroutines.version>
 		<mockk.version>1.10.3-jdk8</mockk.version>
 		<mockito-core.version>3.8.0</mockito-core.version>
-		<spring.version>5.3.5</spring.version>
+		<spring.version>5.3.26</spring.version>
 		<spring-data-bom.version>2020.0.5</spring-data-bom.version>
 		<spring-security-bom.version>5.4.5</spring-security-bom.version>
 		<reactor.version>2020.0.13</reactor.version>