FIX: conda -> pip for collab compat

Author: mmcky

lectures/troubleshooting.md

@@ -46,8 +46,8 @@ You also need to keep the external code libraries, such as [QuantEcon.py](https:
 
 For this task you can either
 
-* use conda install -y quantecon on the command line, or
-* execute !conda install -y quantecon within a Jupyter notebook.
+* use `pip install --upgrade quantecon` on the command line, or
+* execute `!pip install --upgrade quantecon` within a Jupyter notebook.
 
 If your local environment is still not working you can do two things.