fixed tutorial bug that would throw error (ronreiter#692)

the comments (lines 84-85) were hashtags instead of double forward slashes so the compiler (or whatever checks the program) would throw an error when the user has done nothing wrong

Author: slushie0

tutorials/learn-cpp.org/en/if-else.md

@@ -81,8 +81,8 @@ int main()
 
     for(int i = 0; i < 5; i++)
     {        
-        # your code goes here. 
-        # use a if else block to classify the person as Child / Adult / Retired
+        // your code goes here. 
+        // use a if else block to classify the person as Child / Adult / Retired
     }
     return 0;
 }
@@ -121,4 +121,4 @@ int main()
         }
     }
     return 0;
-}
+}