Declare destructor of satcheck_minisat2_baset using override

Because this matches the current coding standards, removes a warning
from clang-tidy and points out that this is overriding a base class
destructor.

Author: thomasspriggs

src/solvers/sat/satcheck_minisat2.h

@@ -30,7 +30,7 @@ class satcheck_minisat2_baset : public cnf_solvert, public hardness_collectort
 {
 public:
   explicit satcheck_minisat2_baset(message_handlert &message_handler);
-  virtual ~satcheck_minisat2_baset();
+  ~satcheck_minisat2_baset() override;
 
   tvt l_get(literalt a) const override final;