fixed indentation.

main.cpp

@@ -41,9 +41,9 @@ int divide(int a, int b) {
 
 std::unordered_map<char, decltype(&plus)> map {
   {'+', add},
-    {'-', subtract},
-    {'*', multiply},
-    {'/', divide}
+  {'-', subtract},
+  {'*', multiply},
+  {'/', divide}
 };
 
 int evaluate(const std::string &s) {