Added error handling

include/cmd/cmd_truncate.hpp

@@ -21,11 +21,11 @@ namespace fsh {
             std::string filename = args.get<std::string>(0).value();
 
             if(!std::ifstream(filename, std::ios_base::in)) {
-                throw std::runtime_error("File does not exist");
+                throw util::FileExistsError();
             }
 
             if(!std::ofstream(filename, std::ios_base::out)) {
-                throw std::runtime_error("Failed to truncate");
+                throw util::CmdError("Failed to truncate");
             }
 
         }