[Backport] Docs: Fix formatting of command line instructions

Sphinx turned the double dash into a long dash. A user reported issues
with running the command after copy&pasting it.

(cherry picked from commit 90ab1f19f0)

docs/source/releases/v0.7.rst

 
     The reviews app has not been under migration control so far. Please ensure
     you follow South's guidelines on how to `convert an app`_. Essentially,
-    you will have to run:
-
-        $ ./manage.py migrate reviews 0001 --fake
+    you will have to run: ``$ ./manage.py migrate reviews 0001 --fake``
 
 .. warning::