fix link to issue

issues/python-ex2-issue.md

@@ -13,7 +13,7 @@ The class [time_window.py](REPO_URL/python/exercise2/time_window.py) is the init
 with the start time, the final time, and the delta (the duration of a single 
 experiment). From these input the number of experiments needed, and the start 
 and stop for both the model and the window are calculated.
-The script [run_test.py](REPO_URL/python/exercise/run_test.py) provided by the lab group
+The script [run_test.py](REPO_URL/python/exercise2/run_test.py) provided by the lab group
 can be used to demonstrate the bug: run_test.py initializes the class and prints
 the window and model times.