Deadlink to SQL-03 specs

[shtukas]

The link to the SQL-03 specs ( http://savage.net.au/SQL/sql-2003-1.bnf.html ) found in https://github.com/google/lovefield/blob/master/docs/spec/00_intro.md is 404.

[shtukas]

Just noticed that there is an open PR for it :)
#200

And that it was a duplicated issue: #199