Change the Dart Plugin version to match the next version of the Flutter IJ plugin to get them in sync. (#78)

This decision still needs team buy-in.

https://plugins.jetbrains.com/plugin/9212-flutter/edit/versions

Author: jwren

third_party/gradle.properties

@@ -7,7 +7,7 @@ pluginName = Dart
 pluginId = Dart
 
 # SemVer format -> https://semver.org
-pluginVersion = 251.30000.0
+pluginVersion = 89.0
 
 # TODO(https://github.com/flutter/dart-intellij-third-party/issues/23) Add a changelog
 # Not currently used in the build.gradle.kts file: