fix broken paper link

Author: mikeferguson

_posts/2020-04-09-robot-calibration-for-ros.html

@@ -94,7 +94,7 @@
 </center>
 <br />
 One of the major benefits of the system is the reliability and speed. On the
-<a href="https://fetchrobotics.com/wp-content/uploads/2018/04/Fetch-and-Freight-Workshop-Paper.pdf">Fetch</a>
+<a href="/{{ site.baseurl }}assets/papers/Fetch-and-Freight-Workshop-Paper.pdf">Fetch</a>
 robot, we only needed to capture 100 poses of the arm/head to calibrate the system. This takes only 8
 minutes, and the calibration step typically takes less than a minute. One of my interns, Niharika Arora,
 ran a series of experiments in which we reduce the number of poses down to 25, meaning that capture and