fix deprecatino warning in build.gradle

kontor-spring/build.gradle

@@ -40,7 +40,9 @@ repositories {
     maven { setUrl("https://maven.vaadin.com/vaadin-addons") }
 }
 
-sourceCompatibility = '17'
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+}
 
 configurations {
     developmentOnly
@@ -152,7 +154,7 @@ bootRun {
 }
 
 task dockerImage(type: Exec) {
-    dependsOn["bootJar"]
+    dependsOn(bootJar)
     commandLine "docker", "build", ".", "-t", "kontor:${project.version}", "-t", "kontor"
 }