Bump spring-boot-gradle-plugin from 2.2.1.RELEASE to 2.2.4.RELEASE

Bumps [spring-boot-gradle-plugin](https://github.com/spring-projects/spring-boot) from 2.2.1.RELEASE to 2.2.4.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.2.1.RELEASE...v2.2.4.RELEASE)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

build.gradle

@@ -1,6 +1,6 @@
 buildscript {
 	ext {
-		springBootVersion = '2.2.1.RELEASE'
+		springBootVersion = '2.2.4.RELEASE'
 	}
 	repositories {
 		mavenCentral()