fix typo

matlab/reporting/@graph/graph.m

@@ -100,7 +100,7 @@ assert(isint(o.legend_font_size), '@graph.graph: legend_font_size must be an int
 assert(islogical(o.zeroline), '@graph.graph: zeroline must be either true or false');
 assert(isfloat(o.shade_opacity) && length(o.shade_opacity)==1 && ...
        o.shade_opacity >= 0 && o.shade_opacity <= 1, ...
-       '@graph.graph: o.shade_opacity must be a real in [0 1]']);
+       '@graph.graph: o.shade_opacity must be a real in [0 1]');
 valid_legend_locations = ...
     {'North', 'South', 'East', 'West', ...
      'NorthEast', 'SouthEast', 'NorthWest', 'SouthWest', ...