Fix calculation of "the sum of all the numbers with odd squares under 1000" in HOF.md

The algorithm to "Find the sum of all the numbers with odd squares under 1000" is wrong. It was calculating the sum of odd squares under 1000.

Author: lpascoali

src/fn/hof.md

@@ -26,18 +26,17 @@ fn main() {
             break;
         } else if is_odd(n_squared) {
             // Accumulate value, if it's odd
-            acc += n_squared;
+            acc += n;
         }
     }
     println!("imperative style: {}", acc);
 
     // Functional approach
-    let sum_of_squared_odd_numbers: u32 =
-        (0..).map(|n| n * n)                             // All natural numbers squared
-             .take_while(|&n_squared| n_squared < upper) // Below upper limit
-             .filter(|&n_squared| is_odd(n_squared))     // That are odd
-             .sum();                                     // Sum them
-    println!("functional style: {}", sum_of_squared_odd_numbers);
+    let sum: u32 =
+        (0..).take_while(|&n| n * n < upper) // Below upper limit
+             .filter(|&n| is_odd(n * n))     // That are odd
+             .sum();                         // Sum them
+    println!("functional style: {}", sum);
 }
 ```