fixup! Use auto for iterator types

Author: romainbrenguier

src/solvers/prop/prop_conv.cpp

@@ -172,7 +172,7 @@ literalt prop_conv_solvert::convert(const exprt &expr)
   }
 
   // check cache first
-  auto result = cache.insert(std::pair<exprt, literalt>(expr, literalt()));
+  auto result = cache.insert({expr, literalt()});
 
   if(!result.second)
     return result.first->second;