Fix codestyle

src/main.cpp

@@ -14,7 +14,7 @@ int main() {
     const int result{evaluate(user_input)};
     std::cout << "Result is: " << result << '\n';
   } catch (const std::invalid_argument& e){
-    std::cout<<"encountered invalid argument"<< e.what()<<std::endl;
+    std::cout << "encountered invalid argument" << e.what() << "\n";
     return -1;
   }