Update bitflags, other dependencies

Bitflags changed its macro codegen from creating constants to associated
constants on structs.

Upgrade path:

Update code from:

```rust
use serenity::model::permissions::{ADD_REACTIONS, MANAGE_MESSAGES};

foo(vec![ADD_REACTIONS, MANAGE_MESSAGES]);
```

to:

```rust
use serenity::model::Permissions;

foo(vec![Permissions::ADD_REACTIONS, Permissions::MANAGE_MESSAGES]);
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/model/user.rs b/src/model/user.rs
index fb6acf0..a214b3d 100644
--- a/src/model/user.rs
+++ b/src/model/user.rs
@@ -176,10 +176,10 @@ impl CurrentUser {
     /// #
     /// # let mut cache = CACHE.write().unwrap();
     ///
-    /// use serenity::model::permissions::*;
+    /// use serenity::model::Permissions;
     ///
     /// // assuming the cache has been unlocked
-    /// let url = match cache.user.invite_url(READ_MESSAGES | SEND_MESSAGES | EMBED_LINKS) {
+    /// let url = match cache.user.invite_url(Permissions::READ_MESSAGES | Permissions::SEND_MESSAGES | Permissions::EMBED_LINKS) {
     ///     Ok(v) => v,
     ///     Err(why) => {
     ///         println!("Error getting invite url: {:?}", why);