Update README to point to SQL:2016, instead of 2011

This was discussed in apache#125, but we forgot to update the README at the time.

Author: nickolay

README.md

@@ -47,10 +47,8 @@ published regularly since. Most revisions have added significant new features to
 the language, and as a result no database claims to support the full breadth of
 features. This parser currently supports most of the SQL-92 syntax, plus some
 syntax from newer versions that have been explicitly requested, plus some MSSQL-
-and PostgreSQL-specific syntax. Whenever possible, the [online SQL:2011
-grammar][sql-2011-grammar] is used to guide what syntax to accept. (We will
-happily accept changes that conform to the SQL:2016 syntax as well, but that
-edition's grammar is not yet available online.)
+and PostgreSQL-specific syntax. Whenever possible, the [online SQL:2016
+grammar][sql-2016-grammar] is used to guide what syntax to accept.
 
 Unfortunately, stating anything more specific about compliance is difficult.
 There is no publicly available test suite that can assess compliance
@@ -105,8 +103,8 @@ If you are unable to submit a patch, feel free to file an issue instead. Please
 try to include:
 
   * some representative examples of the syntax you wish to support or fix;
-  * the relevant bits of the [SQL grammar][sql-2011-grammar], if the syntax is
-    part of SQL:2011; and
+  * the relevant bits of the [SQL grammar][sql-2016-grammar], if the syntax is
+    part of SQL:2016; and
   * links to documentation for the feature for a few of the most popular
     databases that support it.
 
@@ -123,5 +121,5 @@ resources.
 [DataFusion]: https://github.com/apache/arrow/tree/master/rust/datafusion
 [LocustDB]: https://github.com/cswinter/LocustDB
 [Pratt Parser]: https://tdop.github.io/
-[sql-2011-grammar]: https://jakewheat.github.io/sql-overview/sql-2011-foundation-grammar.html
+[sql-2016-grammar]: https://jakewheat.github.io/sql-overview/sql-2016-foundation-grammar.html
 [sql-standard]: https://en.wikipedia.org/wiki/ISO/IEC_9075