Add maven-compler-plugin to starter POM

Add maven-compler-plugin to starter POM in an attempt to fix drone.io
errors downstream.

spring-boot-starters/spring-boot-starter-parent/pom.xml

@@ -290,6 +290,11 @@
 				</plugin>
 			</plugins>
 		</pluginManagement>
+		<plugins>
+			<plugin>
+				<artifactId>maven-compiler-plugin</artifactId>
+			</plugin>
+		</plugins>
 	</build>
 	<profiles>
 		<profile>