don't rely on rubyUtils.gradle loading the versions (logstash-plugins#19)

Author: jsvd

build.gradle

@@ -6,6 +6,9 @@ buildscript {
         mavenCentral()
         gradlePluginPortal()
     }
+    dependencies {
+      classpath "org.yaml:snakeyaml:2.2"
+    }
 }
 
 plugins {
@@ -14,10 +17,14 @@ plugins {
 }
 
 ext {
-    snakeYamlVersion = '2.2'
     shadowGradlePluginVersion = '8.1.1'
 }
 
+// load versions.yml from core before loading rubyUtils.gradle
+import org.yaml.snakeyaml.Yaml
+
+def versionsFile = file(LOGSTASH_CORE_PATH + "/../versions.yml")
+gradle.ext.versions = new Yaml().load(versionsFile.text)
 
 apply from: LOGSTASH_CORE_PATH + "/../rubyUtils.gradle"
 
@@ -60,7 +67,7 @@ dependencies {
     implementation fileTree(dir: LOGSTASH_CORE_PATH, include: "**/logstash-core.jar")
 
     testImplementation 'junit:junit:4.12'
-    testImplementation 'org.jruby:jruby-complete:9.4.7.0'
+    testImplementation "org.jruby:jruby-complete:${gradle.ext.versions.jruby.version}"
 }
 
 clean {