bpo-39348: Fix code highlight for the SOCK_NONBLOCK example (GH-18018)


The previous double colon was wrongly place directly after Therefore.
Which produced a block without syntax highlighting. This fixes it
by separating the double colon from the text. As a result, sphinx now
properly highlights the python code.

https://bugs.python.org/issue39348
(cherry picked from commit fad8b5674c66d9e00bb788e30adddb0c256c787b)

Co-authored-by: Oz N Tiram <oz.tiram@noris.de>
diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst
index ae82e43..c72f22b 100644
--- a/Doc/library/socket.rst
+++ b/Doc/library/socket.rst
@@ -548,7 +548,9 @@
       When :const:`SOCK_NONBLOCK` or :const:`SOCK_CLOEXEC`
       bit flags are applied to *type* they are cleared, and
       :attr:`socket.type` will not reflect them.  They are still passed
-      to the underlying system `socket()` call.  Therefore::
+      to the underlying system `socket()` call.  Therefore,
+
+      ::
 
           sock = socket.socket(
               socket.AF_INET,