Fix pyhelpers import in TLE Propagation example

examples/TLE Propagation.ipynb

@@ -51,7 +51,7 @@
       "import orekit\n",
       "orekit.initVM()\n",
       "\n",
-      "from setup_orekit_curdir import setup_orekit_curdir\n",
+      "from orekit.pyhelpers import setup_orekit_curdir\n",
       "setup_orekit_curdir()"
      ],
      "language": "python",