Send users to the ChirpNextBuild page for updates

Until the proper Download page includes links to the CHIRP-next build,
we should send them to ChirpNextBuild, which includes the download
link and may include updated information over time which would be
good to get in front of early adopters as well.

This also makes us warn the user to quit CHIRP before installing the
next build, as that is a common stumbling block for users.

chirp/wxui/main.py

@@ -1243,11 +1243,13 @@ def display_update_notice(version):
 
     CONF.set_int("last_update_check", int(time.time()), "state")
 
+    url = 'https://chirp.danplanet.com/projects/chirp/wiki/ChirpNextBuild'
     msg = _('A new CHIRP version is available. Please visit the '
             'website as soon as possible to download it!')
     d = wx.MessageDialog(None, msg, _('New version available'),
                          style=wx.OK | wx.CANCEL | wx.ICON_INFORMATION)
     visit = d.ShowModal()
     if visit == wx.ID_OK:
-        webbrowser.open('https://chirp.danplanet.com/'
-                        'projects/chirp/wiki/Download')
+        wx.MessageBox(_('Please be sure to quit CHIRP before installing '
+                        'the new version!'))
+        webbrowser.open(url)