[utils] Add common user agents map

youtube_dl/utils.py

@@ -86,6 +86,11 @@ std_headers = {
 }
 
 
+USER_AGENTS = {
+    'Safari': 'Mozilla/5.0 (X11; Linux x86_64; rv:10.0) AppleWebKit/533.20.25 (KHTML, like Gecko) Version/5.0.4 Safari/533.20.27',
+}
+
+
 NO_DEFAULT = object()
 
 ENGLISH_MONTH_NAMES = [