Add support for chrome_duration option

Add support for chrome_duration option

@@ -43,6 +43,13 @@ class Chrome implements \JsonSerializable
 */
 private $image;
 
+/**
+* Changes chrome push display time. Set to 0 to display push until user interacts with it
+*
+* @var int
+*/
+private $duration;
+
 /**
 * Utility function used to create a new Chrome instance.
 *
@@ -76,7 +83,7 @@ public function getIcon()
 /**
 * Gets the header of the message.
 *
-* @var string The header of the message.
+* @return string The header of the message.
 */
 public function getTitle()
 {
@@ -86,12 +93,22 @@ public function getTitle()
 /**
 * Gets the image of the message.
 *
-* @var string The image of the message.
+* @return string The image of the message.
 */
 public function getImage()
 {
 return $this->image;
 }
+
+/**
+* Gets the duration
+*
+* @return int
+*/
+public function getDuration()
+{
+return $this->duration;
+}
 
 /**
 * {@inheritdoc}
@@ -104,9 +121,9 @@ public function jsonSerialize()
 isset($this->icon) ? $json['chrome_icon'] = $this->icon : false;
 isset($this->title) ? $json['chrome_title'] = $this->title : false;
 isset($this->image) ? $json['chrome_image'] = $this->image : false;
+isset($this->duration) ? $json['chrome_duration'] = $this->duration : false;
 
 return $json;
-
 }
 
 /**
@@ -164,4 +181,18 @@ public function setImage($image)
 
 return $this;
 }
+
+/**
+* Sets the duration
+*
+* @param $duration
+*
+* @return \Gomoob\Pushwoosh\Model\Notification\Chrome this instance.
+*/
+public function setDuration($duration)
+{
+$this->duration = $duration;
+
+return $this;
+}
 }