Make sure to not archive PR JAR artifacts.

Jenkinsfile

@@ -2,6 +2,8 @@ pipeline {
   agent none
   stages {
     stage('Build') {
+      GIT_BRANCH = sh(returnStdout: true, script: 'git rev-parse --abbrev-ref HEAD').trim()
+
       agent {
         docker {
           image 'velocitypowered/openjdk8-plus-git:slim'
@@ -10,9 +12,11 @@ pipeline {
       }
       steps {
         sh './gradlew build --no-daemon'
+        if (GIT_BRANCH == "master") {
           archiveArtifacts 'proxy/build/libs/*-all.jar,api/build/libs/*-all.jar'
         }
       }
+    }
     stage('Deploy') {
       when {
         expression {