Use proper rst markup

underscores are not understood the same way they are in markdown

Author: greg0ire

contributing/code/stack_trace.rst

@@ -91,7 +91,7 @@ Several things need to be paid attention to when picking a stack trace
 from your development environment through a web browser:
 
 1. Are there several exceptions? If yes, the most interesting one is
-   often exception 1/n which, is shown _last_ in the example below (it
+   often exception 1/n which, is shown *last* in the example below (it
    is the one marked as exception [1/2]).
 2. Under the "Stack Traces" tab, you will find exceptions in plain
    text, so that you can easily share them in e.g. bug reports. Make