explicitly added dependency javax.servlet-api

pom.xml

@@ -93,6 +93,13 @@
 			<groupId>com.vaadin</groupId>
 			<artifactId>vaadin-spring-boot-starter</artifactId>
 		</dependency>
+		<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
+		<dependency>
+		    <groupId>javax.servlet</groupId>
+		    <artifactId>javax.servlet-api</artifactId>
+<!-- 		    <version>4.0.1</version> -->
+		    <scope>provided</scope>
+		</dependency>
 
 		<dependency>
 			<groupId>com.h2database</groupId>