Typo fix, found while going through the code.

youtube_dl/downloader/common.py

@@ -42,7 +42,7 @@ class FileDownloader(object):
     min_filesize:       Skip files smaller than this size
     max_filesize:       Skip files larger than this size
     xattr_set_filesize: Set ytdl.filesize user xattribute with expected size.
-                        (experimenatal)
+                        (experimental)
     external_downloader_args:  A list of additional command-line arguments for the
                         external downloader.
 

youtube_dl/downloader/rtmp.py

@@ -117,7 +117,7 @@ class RtmpFD(FileDownloader):
             return False
 
         # Download using rtmpdump. rtmpdump returns exit code 2 when
-        # the connection was interrumpted and resuming appears to be
+        # the connection was interrupted and resuming appears to be
         # possible. This is part of rtmpdump's normal usage, AFAIK.
         basic_args = [
             'rtmpdump', '--verbose', '-r', url,