[Hacktoberfest] Ensure the code compiled with java 11 and find places to use new API's from java 11.

[ahmetoz]

Situation
We migrated the app from java 8 to java 11, on: https://github.com/commercetools/commercetools-project-sync/releases/tag/3.12.0

Complication
As we could use java 11, we might benefit of new apis from java 11 in the project.
Also we are not sure if the project is compiling with java 11:

commercetools-project-sync/gradle-scripts/java-compile.gradle

Lines 1 to 6 in 90bfbfa

	sourceCompatibility = 1.8
	targetCompatibility = 1.8
	tasks.withType(JavaCompile) {
	options.encoding = 'UTF-8'
	options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
	}

Resolution
Ensure the code compiled with java 11 and find places to use API's from java 11. If possible refactor code to use new APIs from java 11.