Fix license on expression grammar.

/*

 * This grammar is a tweaked subset of that in Java.g4, which has a

 * BSD license and is redistributed along with this.

 [The "BSD licence"]

 Copyright (c) 2013 Terence Parr, Sam Harwell

 All rights reserved.

 Redistribution and use in source and binary forms, with or without

 modification, are permitted provided that the following conditions

 are met:

 1. Redistributions of source code must retain the above copyright

    notice, this list of conditions and the following disclaimer.

 2. Redistributions in binary form must reproduce the above copyright

    notice, this list of conditions and the following disclaimer in the

    documentation and/or other materials provided with the distribution.

 3. The name of the author may not be used to endorse or promote products

    derived from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*/

grammar BindingExpression;