아래와 같이 pom.xml 설정으로 해결이 가능하다.
방법 1
<properties>
<java.version>1.7</java.version>
<tomcat.version>7.0.78</tomcat.version>
<failOnMissingWebXml>false</failOnMissingWebXml>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
방법 2
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>1.5.3.RELEASE</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<failOnMissingWebXml>false</failOnMissingWebXml>
</configuration>
</plugin>
</plugins>
</build>
참고
https://stackoverflow.com/questions/5351948/webxml-attribute-is-required-error-in-maven
[출처] http://1004lucifer.blogspot.com/2017/06/maven-package-webxml-attribute-is.html