doc: Update collections exercises instruction to match the standard naming

exercises/collections/hashmap1.rs

@@ -8,7 +8,7 @@
 //
 // Make me compile and pass the tests!
 //
-// Execute the command `rustlings hint collections3` if you need
+// Execute the command `rustlings hint hashmap1` if you need
 // hints.
 
 // I AM NOT DONE
@@ -39,8 +39,6 @@ mod tests {
     #[test]
     fn at_least_five_fruits() {
         let basket = fruit_basket();
-        assert!(basket
-            .values()
-            .sum::<u32>() >= 5);
+        assert!(basket.values().sum::<u32>() >= 5);
     }
 }

exercises/collections/hashmap2.rs

@@ -9,7 +9,7 @@
 //
 // Make me pass the tests!
 //
-// Execute the command `rustlings hint collections4` if you need
+// Execute the command `rustlings hint hashmap2` if you need
 // hints.
 
 // I AM NOT DONE
@@ -75,9 +75,7 @@ mod tests {
     fn greater_than_eleven_fruits() {
         let mut basket = get_fruit_basket();
         fruit_basket(&mut basket);
-        let count = basket
-            .values()
-            .sum::<u32>();
+        let count = basket.values().sum::<u32>();
         assert!(count > 11);
     }
 }

exercises/collections/vec1.rs

@@ -2,7 +2,7 @@
 // Your task is to create a `Vec` which holds the exact same elements
 // as in the array `a`.
 // Make me compile and pass the test!
-// Execute the command `rustlings hint collections1` if you need hints.
+// Execute the command `rustlings hint vec1` if you need hints.
 
 // I AM NOT DONE
 

exercises/collections/vec2.rs

@@ -4,7 +4,7 @@
 //
 // Make me pass the test!
 //
-// Execute the command `rustlings hint collections2` if you need
+// Execute the command `rustlings hint vec2` if you need
 // hints.
 
 // I AM NOT DONE