Add maven implicit plugin group ID

Add previously implicit <groupId>org.apache.maven.plugins</groupId>
to plugin declarations.

spring-boot-samples/pom.xml

@@ -57,6 +57,7 @@
 	<build>
 		<plugins>
 			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-eclipse-plugin</artifactId>
 				<configuration>
 					<useProjectReferences>false</useProjectReferences>
@@ -73,6 +74,7 @@
 				</configuration>
 			</plugin>
 			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-surefire-plugin</artifactId>
 				<configuration>
 					<includes>