Upgrade to maven-assembly-plugin 3.1.0

Closes spring-projectsgh-7513

Author: snicoll

spring-boot-dependencies/pom.xml

@@ -196,7 +196,7 @@
 		<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</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>