Update crude installation instructions to properly find get-pipenv.py

Changed the raw-file link for get-pipenv.py so that calling curl would lead to
the actual file instead of a 302 Redirect to the file.

Author: jabagawee

docs/advanced.rst

@@ -199,7 +199,7 @@ To upgrade pipenv at any time::
 
 If you don't even have pip installed, you can use this crude installation method, which will boostrap your whole system::
 
-    $ curl https://github.com/kennethreitz/pipenv/raw/master/get-pipenv.py | python
+    $ curl https://raw.githubusercontent.com/kennethreitz/pipenv/master/get-pipenv.py | python
 
 Congratulations, you now have pip and Pipenv installed!