Support IntelliJ IDEA 2020.1

[snsyzf]

IDEA 2020.1 not support

[philwebb]

@snsyzf I've just committed a fix. If you want to try the latest SNAPSHOT it's available at https://repo.spring.io/snapshot/io/spring/javaformat/spring-javaformat-intellij-plugin/0.0.21-SNAPSHOT/spring-javaformat-intellij-plugin-0.0.21-20200410.061412-5.jar