[BUG] [Spring] Async missing import

Created by: TruthNZ

When specifying

<configOptions>
	<java8>true</java8>
	<dateLibrary>java8</dateLibrary>
	<library>spring-cloud</library>
	<async>true</async>
</configOptions>
<generatorName>spring</generatorName>

the generated API Interface file is missing the import for CompletableFuture (assumably import java.util.concurrent.CompletableFuture;)