Use double quotes in error message (#2112)

On Windows, double quotes are required, because single quotes get served to youtube-dl. (Yes, cmd.exe is crazy like that).
On other system, both double and single quotes are fine, unless the string contains a dollar sign (then you need single quotes).
Since virtually no URLs contain dollar signs, double quotes should do.

youtube_dl/extractor/youtube.py

@@ -1759,6 +1759,6 @@ class YoutubeTruncatedURLIE(InfoExtractor):
             u'Did you forget to quote the URL? Remember that & is a meta '
             u'character in most shells, so you want to put the URL in quotes, '
             u'like  youtube-dl '
-            u'\'http://www.youtube.com/watch?feature=foo&v=BaW_jenozKc\''
-            u' (or simply  youtube-dl BaW_jenozKc  ).',
+            u'"http://www.youtube.com/watch?feature=foo&v=BaW_jenozKc" '
+            u' or simply  youtube-dl BaW_jenozKc  .',
             expected=True)