Maven version prerequisite should be treated as minimum version

[Martin Polden]

According to the Maven documentation (http://maven.apache.org/ref/3.3.3/maven-model/maven.html), the following specifies the minimum required Maven version:

<prerequisites>
  <maven>[version]</maven>
</prerequisites>

However, mvnvm seems to treat it as an absolute version. E.g. when the version is set to 2.2.1, mvnvm will download and run that version, even though a higher version is installed.