Merge pull request #143 from einorler/abstract_pipeline_aggregation

Added abstract pipeline aggregation

src/Aggregation/Pipeline/AbstractPipelineAggregation.php

+<?php
+
+namespace ONGR\ElasticsearchDSL\Aggregation\Pipeline;
+
+use ONGR\ElasticsearchDSL\Aggregation\AbstractAggregation;
+use ONGR\ElasticsearchDSL\Aggregation\Type\MetricTrait;
+
+abstract class AbstractPipelineAggregation extends AbstractAggregation
+{
+    use MetricTrait;
+
+    /**
+     * @var string
+     */
+    private $bucketsPath;
+
+    /**
+     * @param string $name
+     * @param $bucketsPath
+     */
+    public function __construct($name, $bucketsPath)
+    {
+        parent::__construct($name);
+        $this->setBucketsPath($bucketsPath);
+    }
+
+    /**
+     * @return string
+     */
+    public function getBucketsPath()
+    {
+        return $this->bucketsPath;
+    }
+
+    /**
+     * @param string $bucketsPath
+     */
+    public function setBucketsPath($bucketsPath)
+    {
+        $this->bucketsPath = $bucketsPath;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getArray()
+    {
+        return ['buckets_path' => $this->getBucketsPath()];
+    }
+}