Update META-INF/plugin.xml to relax upper bounds

Currently IntelliJ Community builds from git have been renumbered to 126.x so there are no more plugin updates for Scala coming thru.

This means it can't be used/tested under nightly builds of what will be 12.1 or later.
Merge pull request #24 from talios/patch-1

Update META-INF/plugin.xml to relax upper bounds