point to @kalxas correct Twitter handle

Author: tomkralidis

workshop/jupyter/content/notebooks/01-introduction.ipynb

@@ -35,7 +35,7 @@
     "        <td><a href=\"https://twitter.com/justb4\"><img width=\"150\" src=\"https://avatars.githubusercontent.com/u/582630?v=4\"/></a></td>\n",
     "        <td><a href=\"https://twitter.com/ldesousa\"><img width=\"150\" src=\"https://avatars.githubusercontent.com/u/1137878?v=4\"/></a></td>\n",
     "        <td><a href=\"https://twitter.com/francbartoli\"><img width=\"150\" src=\"https://avatars.githubusercontent.com/u/560676?v=4\"/></a></td>\n",
-    "        <td><a href=\"https://twitter.com/kalxas\"><img width=\"150\" src=\"https://avatars.githubusercontent.com/u/383944?v=4\"/></a></td>\n",
+    "        <td><a href=\"https://twitter.com/tzotsos\"><img width=\"150\" src=\"https://avatars.githubusercontent.com/u/383944?v=4\"/></a></td>\n",
     "    </tr>\n",
     "    <tr>\n",
     "        <td>Tom Kralidis</td>\n",