Remove unused import from installation.rst (#1648)

Author: jonatron

docs/installation.rst

@@ -138,7 +138,6 @@ option.
     If using Docker the following will set your ``INTERNAL_IPS`` correctly in Debug mode::
 
         if DEBUG:
-            import os  # only if you haven't already imported this
             import socket  # only if you haven't already imported this
             hostname, _, ips = socket.gethostbyname_ex(socket.gethostname())
             INTERNAL_IPS = [ip[: ip.rfind(".")] + ".1" for ip in ips] + ["127.0.0.1", "10.0.2.2"]