Rename namespace Function keyword to Functions to prevent errors

Signed-off-by: davidarendsen <davidarendsen@hey.com>

src/Functions/Group.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Functions;
+
+use Arendsen\FluxQueryBuilder\Formatters;
+
+class Group extends Base {
+
+    /**
+     * @var array $columns
+     */
+    private $columns;
+
+    /**
+     * @var string $mode
+     */
+    private $mode;
+
+    public function __construct(array $columns, string $mode = 'by')
+    {
+        $this->columns = $columns;
+        $this->mode = $mode;
+    }
+
+    public function __toString()
+    {
+        $array = Formatters::toFluxArrayString([
+            'columns' => $this->columns,
+            'mode' => $this->mode,
+        ]);
+
+        return '|> group(' . $array . ') ';
+    }
+
+}