Correcting initial_loop_bound type

Author: romainbrenguier

src/solvers/refinement/string_refinement.h

@@ -61,7 +61,7 @@ class string_refinementt: public bv_refinementt
   // Base class
   typedef bv_refinementt supert;
 
-  unsigned long initial_loop_bound;
+  unsigned initial_loop_bound;
 
   string_constraint_generatort generator;