title: Unknown referenced nature: org.springframework.ide.eclipse.core.springnature
body: <p>In STS 4, my Java 10 Spring Boot 2.1 project warns me:</p>
  
  <blockquote>
    <p>Unknown referenced nature:
    org.springframework.ide.eclipse.core.springnature</p>
  </blockquote>
  
  <p>How can I fix this?</p>