Update to Spring Boot 2.4.0-M3

Closes gh-123

gradle.properties

@@ -1,5 +1,5 @@
 version=0.0.2-SNAPSHOT
-springBootVersion=2.4.0-M2
+springBootVersion=2.4.0-M3
 org.gradle.jvmargs=-Xmx3g -XX:MaxPermSize=2048m -XX:+HeapDumpOnOutOfMemoryError
 org.gradle.parallel=true
 org.gradle.caching=true