fix dead link

Author: Till Beemelmanns

section_1_introduction_and_tools/3_introduction_to_ros1.ipynb

@@ -412,7 +412,7 @@
    "id": "b8467f63-e4f1-4d68-964b-e9f4d3059b0c",
    "metadata": {},
    "source": [
-    "Upon calling the `.subscribe()` function, `jupyter-ros` will create a handle to a [rospy](http://wiki.ros.org/rospy) subscriber thread. Hence, JupyRos wraps the `rospy` functionality and extends it for Jupyter Notebook. Note that we did not use the rospy-way of creating a subscriber. We recommend to have a look on the [official documentation](https://wiki.ros.org/ROS/Tutorials/WritingPublisherSubscriber) for rospy, in order to understand how to setup a publisher subscriber in Python. But we will also cover this in the upcoming learning units in this MOOC"
+    "Upon calling the `.subscribe()` function, `jupyter-ros` will create a handle to a [rospy](http://wiki.ros.org/rospy) subscriber thread. Hence, JupyRos wraps the `rospy` functionality and extends it for Jupyter Notebook. Note that we did not use the rospy-way of creating a subscriber. We recommend to have a look on the [official documentation](https://wiki.ros.org/ROS/Tutorials/WritingPublisherSubscriber%28python%29) for rospy, in order to understand how to setup a publisher subscriber in Python. But we will also cover this in the upcoming learning units in this MOOC"
    ]
   },
   {