Add Spring Integration Sample

Demonstrates how `IntegrationFlow` can be exposed as a `Function`

* Upgrade to the latest dependencies

* Polishing
Resolves #214

spring-cloud-function-samples/function-sample-spring-integration/src/main/java/example/FunctionSampleSpringIntegrationApplication.java

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+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package example;
+
+import java.util.function.Function;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.integration.dsl.IntegrationFlows;
+import org.springframework.integration.handler.LoggingHandler;
+import org.springframework.messaging.Message;
+
+@SpringBootApplication
+public class FunctionSampleSpringIntegrationApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(FunctionSampleSpringIntegrationApplication.class, args);
+	}
+
+	@Bean
+	public IntegrationFlow uppercaseFlow() {
+		return IntegrationFlows.from(MessageFunction.class, "uppercase")
+				.<String, String>transform(String::toUpperCase)
+				.logAndReply(LoggingHandler.Level.WARN);
+	}
+
+	public interface MessageFunction extends Function<Message<String>, Message<String>> {
+
+	}
+
+}