add comment function in column builder in yii2 2.0.7

changed.diff

diff --git a/ColumnSchemaBuilder.php b/ColumnSchemaBuilder.php
index bfa26bd..45ca8f5 100644
--- a/ColumnSchemaBuilder.php
+++ b/ColumnSchemaBuilder.php
@@ -51,6 +51,7 @@ class ColumnSchemaBuilder extends Object
      * @since 2.0.7
      */
     protected $isUnsigned = false;
+    protected $comment;


     /**
@@ -109,6 +110,11 @@ class ColumnSchemaBuilder extends Object
         return $this;
     }

+    public function comment($comment){
+        $this->comment = $comment;
+        return $this;
+    }
+
     /**
      * Marks column as unsigned.
      * @return $this
@@ -145,7 +151,17 @@ class ColumnSchemaBuilder extends Object
             $this->buildNotNullString() .
             $this->buildUniqueString() .
             $this->buildDefaultString() .
-            $this->buildCheckString();
+            $this->buildCheckString().
+            $this->buildCommentString();
+    }
+
+    /**
+     * Builds the not null constraint for the column.
+     * @return string returns 'NOT NULL' if [[isNotNull]] is true, otherwise it returns an empty string.
+     */
+    protected function buildCommentString()
+    {
+        return $this->comment ? " COMMENT '$this->comment'": '';
     }