Wrap argument to \sv with braces inside expansion

* This addresses complaints about ! Double superscript. (or subscript)
  when compiling in XeLaTeX mode.

Author: chbrown

sp.cls

@@ -538,7 +538,7 @@
 
 \newcommand{\email}[1]{\href{mailto:#1}{#1}}
 
-\providecommand{\sv}[1]{\ensuremath{\llbracket #1 \rrbracket}}
+\providecommand{\sv}[1]{\ensuremath{\llbracket{#1}\rrbracket}}
 
 %=====================================================================
 %=========================== linguex settings ========================