Fix some typos in the documentation

src/libcollections/btree/map.rs

@@ -313,7 +313,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     // 2) While ODS may potentially return the pair we *just* inserted after
     // the split, we will never do this. Again, this shouldn't effect the analysis.
 
-    /// Inserts a key-value pair from the map. If the key already had a value
+    /// Inserts a key-value pair into the map. If the key already had a value
     /// present in the map, that value is returned. Otherwise, `None` is returned.
     ///
     /// # Examples

src/libcollections/vec_map.rs

@@ -576,7 +576,7 @@ impl<V> VecMap<V> {
         }
     }
 
-    /// Inserts a key-value pair from the map. If the key already had a value
+    /// Inserts a key-value pair into the map. If the key already had a value
     /// present in the map, that value is returned. Otherwise, `None` is returned.
     ///
     /// # Examples

src/libstd/collections/hash/map.rs

@@ -1107,7 +1107,7 @@ impl<K, V, S> HashMap<K, V, S>
         self.search_mut(k).map(|bucket| bucket.into_mut_refs().1)
     }
 
-    /// Inserts a key-value pair from the map. If the key already had a value
+    /// Inserts a key-value pair into the map. If the key already had a value
     /// present in the map, that value is returned. Otherwise, `None` is returned.
     ///
     /// # Examples