fetch: use single quotes around command hint

Windows command lines use double quotes to quote arguments with spaces.
This change is in a series to unify around using single quotes around
commands, and double quotes around interior arguments.

hgext/fetch.py

@@ -61,7 +61,7 b" def fetch(ui, repo, source='default', **"
         branchnode = None
     if parent != branchnode:
         raise error.Abort(_('working directory not at branch tip'),
-                         hint=_('use "hg update" to check out branch tip'))
+                         hint=_("use 'hg update' to check out branch tip"))
 
     wlock = lock = None
     try:

tests/test-fetch.t

@@ -339,7 +339,7 b' pull in change on different branch than '
   (branches are permanent and global, did you want a bookmark?)
   $ hg -R n2 fetch -m merge n1
   abort: working directory not at branch tip
-  (use "hg update" to check out branch tip)
+  (use 'hg update' to check out branch tip)
   [255]
 
 parent should be 0 (fetch did not update or merge anything)