Make plusarg_reader default args work with VCS (#765)

Resolves #764

vsrc/plusarg_reader.v

@@ -2,7 +2,7 @@
 
 // No default parameter values are intended, nor does IEEE 1800-2012 require them (clause A.2.4 param_assignment),
 // but Incisive demands them. These default values should never be used.
-module plusarg_reader #(string FORMAT="borked", int DEFAULT=0) (
+module plusarg_reader #(string FORMAT="borked=%d", int DEFAULT=0) (
    output [31:0] out
 );