Fix Maven warning in samples

Closes gh-7716

Author: snicoll

spring-boot-samples/pom.xml

@@ -228,6 +228,11 @@
 						</lifecycleMappingMetadata>
 					</configuration>
 				</plugin>
+				<plugin>
+					<groupId>org.apache.maven.plugins</groupId>
+					<artifactId>maven-enforcer-plugin</artifactId>
+					<version>1.4</version>
+				</plugin>
 			</plugins>
 		</pluginManagement>
 	</build>