Support JDK 14

[Frederik Hahne]

Overview of the feature request

Right now both gradle and maven build files still enforce an upper bound for JDK 13. In the main generator we have already switched to JDK 14.

• generator-jhipster-micronaut/generators/server/templates/build.gradle.ejs

  Line 62 in 736f1b4

   assert System.properties["java.specification.version"] == "1.8" || "11" || "12" || "13" 

• generator-jhipster-micronaut/generators/server/templates/pom.xml.ejs

  Line 872 in 736f1b4

   <version>[1.8,13)</version> 

Motivation for or Use Case

For example the heroku subgen asks for the jdk to use and assumes jdk 14 is the latest supported version (as we don't overwrite that prompt). Furthermore we should support the latest supported version if possible.

Related issues or PR

• #126