Merge pull request #42 from silviapfeiffer/default_line_align

Be consistent with the default values.

webvtt.html

@@ -1665,7 +1665,7 @@ <h4>WebVTT cue settings</h4>
   position. The positioning is calculated relative to the <a title="text track cue line start alignment">start</a>,
   <a title="text track cue line middle alignment">middle</a>, or <a title="text track cue line end alignment">end</a>
   of the cue box, depending on the <a>text track cue line alignment</a> value -
-  <a title="text track cue line middle alignment">middle</a> by default.
+  <a title="text track cue line start alignment">start</a> by default.
   The position can be given either as a percentage of the video dimension
   or as a line number. Line numbers are based on the size of the first line of the
   cue. Positive line numbers count from the start of the video frame (the first