Migrate import statements and macros to Rust 2018.

src/embedded_flash/buffer.rs

@@ -14,6 +14,7 @@
 
 use super::{Index, Storage, StorageError, StorageResult};
 use alloc::boxed::Box;
+use alloc::vec;
 
 pub struct BufferStorage {
     storage: Box<[u8]>,

src/embedded_flash/store/format.rs

@@ -14,6 +14,7 @@
 
 use super::super::{Index, Storage};
 use super::{bitfield, StoreConfig, StoreEntry, StoreError};
+use alloc::vec;
 use alloc::vec::Vec;
 
 /// Whether a user entry is a replace entry.

src/embedded_flash/store/mod.rs

@@ -169,6 +169,7 @@ use crate::embedded_flash::BufferStorage;
 #[cfg(any(test, feature = "ram_storage"))]
 use alloc::boxed::Box;
 use alloc::collections::BTreeMap;
+use alloc::vec;
 use alloc::vec::Vec;
 
 /// Configures a store.