Upgrade to JDK9 compatible maven plugins

This commit uses the SNAPSHOT preview of the enforcer and assembly
plugins as the latest ones available are not compatible with JDK9

Author: snicoll

spring-boot-dependencies/pom.xml

@@ -196,13 +196,13 @@
 		<exec-maven-plugin.version>1.5.0</exec-maven-plugin.version>
 		<git-commit-id-plugin.version>2.2.2</git-commit-id-plugin.version>
 		<maven-antrun-plugin.version>1.8</maven-antrun-plugin.version>
-		<maven-assembly-plugin.version>2.6</maven-assembly-plugin.version>
+		<maven-assembly-plugin.version>3.1.0-SNAPSHOT</maven-assembly-plugin.version>
 		<maven-clean-plugin.version>3.0.0</maven-clean-plugin.version>
 		<maven-compiler-plugin.version>3.6.2</maven-compiler-plugin.version>
 		<maven-dependency-plugin.version>2.10</maven-dependency-plugin.version>
 		<maven-deploy-plugin.version>2.8.2</maven-deploy-plugin.version>
 		<maven-eclipse-plugin.version>2.10</maven-eclipse-plugin.version>
-		<maven-enforcer-plugin.version>1.4</maven-enforcer-plugin.version>
+		<maven-enforcer-plugin.version>3.0.0-SNAPSHOT</maven-enforcer-plugin.version>
 		<maven-failsafe-plugin.version>2.18.1</maven-failsafe-plugin.version>
 		<maven-install-plugin.version>2.5.2</maven-install-plugin.version>
 		<maven-invoker-plugin.version>3.0.0</maven-invoker-plugin.version>

spring-boot-parent/pom.xml

@@ -651,6 +651,13 @@
 						<enabled>true</enabled>
 					</snapshots>
 				</pluginRepository>
+				<pluginRepository>
+					<id>apache-snapshot</id>
+					<url>http://repository.apache.org/snapshots</url>
+					<snapshots>
+						<enabled>true</enabled>
+					</snapshots>
+				</pluginRepository>
 			</pluginRepositories>
 		</profile>
 		<profile>

spring-boot-samples/pom.xml

@@ -263,5 +263,12 @@
 				<enabled>false</enabled>
 			</snapshots>
 		</pluginRepository>
+		<pluginRepository>
+			<id>apache-snapshot</id>
+			<url>http://repository.apache.org/snapshots</url>
+			<snapshots>
+				<enabled>true</enabled>
+			</snapshots>
+		</pluginRepository>
 	</pluginRepositories>
 </project>