Add missing brace to return example code

fixes arduino/Arduino#6562

Author: per1234

Language/Structure/Control Structure/return.adoc

@@ -55,6 +55,7 @@ A function to compare a sensor input to a threshold
  int checkSensor(){
     if (analogRead(0) > 400) {
         return 1;
+    }
     else{
         return 0;
     }