Update version to 0.2.0

Dropped the `-alpha` suffix, because I think the plugin is ready to be
published to JetBrains' default plugin repository, making it available
to all JetBrains Marketplace users.

gradle.properties

@@ -4,7 +4,7 @@ pluginGroup = nl.dirkgroot.structurizr-dsl-plugin
 pluginName = Structurizr DSL Language Support
 pluginRepositoryUrl = https://github.com/dirkgroot/structurizr-dsl-intellij-plugin
 # SemVer format -> https://semver.org
-pluginVersion = 0.1.4-alpha
+pluginVersion = 0.2.0
 
 # Supported build number ranges and IntelliJ Platform versions -> https://plugins.jetbrains.com/docs/intellij/build-number-ranges.html
 pluginSinceBuild = 223