making-the-grade: Fix introduction.md (#751)

Variable-name in syntax of std::array and std::vector was in the wrong position in the commented lines of the examples.

exercises/concept/making-the-grade/.docs/introduction.md

@@ -15,7 +15,7 @@ Look at these examples to see the two container types' initializations:
 #include<array>
 #include <string>
 
-// std::array variable_name<element_type, size> {list of elements}
+// std::array<element_type, size> variable_name {list of elements}
 std::array<std::string, 3> indie_rock {"yeah", "yeah", "yeah"};
 // indie_rock contains the elements "yeah" three times
 ```
@@ -26,7 +26,7 @@ You do not need to specify a size:
 ```cpp
 #include<vector>
 
-// std::vector variable_name<element_type> {list of elements}
+// std::vector<element_type> variable_name {list of elements}
 std::vector<int> countdown {3, 2, 1};
 // my_vector contains the elements 3, 2 and 1
 ```