Update java runtime version to support App Engine (#3404)

* Update java runtime version to support App Engine

* Adding version number for maven-compiler

* Update maven-compiler configuration

* Update pom.xml

* Update App engine properties

* Update pom.xml

java/demo/pom.xml

@@ -16,8 +16,8 @@
     <app.deploy.project>libphonenumber-hrd</app.deploy.project>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
-    <maven.compiler.source>1.8</maven.compiler.source>
-    <maven.compiler.target>1.8</maven.compiler.target>
+    <maven.compiler.source>11</maven.compiler.source>
+    <maven.compiler.target>11</maven.compiler.target>
     <maven.compiler.showDeprecation>true</maven.compiler.showDeprecation>
     <archiveClasses>true</archiveClasses>
     <soy.root>${project.basedir}/src/main/resources/com/google/phonenumbers/demo</soy.root>

java/demo/src/main/webapp/WEB-INF/appengine-web.xml

@@ -2,7 +2,7 @@
 <appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
   <application>libphonenumber-hrd</application>
   <version>1</version>
-  <runtime>java8</runtime>
+  <runtime>java11</runtime>
   <threadsafe>true</threadsafe>
 
   <!-- Configure java.util.logging -->