deps: Update to a more recent rocket and rust toolchain

With this patch, Plume will be use a more up-to-date revision of
Rocket, that works with nightly-2018-07-17. It may have been able to
make it work with a more recent revision, but it turns out rocket has
introduced several breaking changes so I’d rather fix those.

Besides updating rocket_i18n and rocket_csrf to use the same revision
than Plume, this patch deals with the new implementation of the
Uri<'_> type. It silents a class of warnings, to deal with a change in
rustc which affects diesel. This latter change should be reverted as
soon as diesel releases a new version of its crate.

plume-models/src/comments.rs

@@ -57,7 +57,7 @@ impl Comment {
     }
 
     pub fn get_post(&self, conn: &PgConnection) -> Post {
-        Post::get(conn, self.post_id).unwrap()        
+        Post::get(conn, self.post_id).unwrap()
     }
 
     pub fn count_local(conn: &PgConnection) -> usize {

plume-models/src/lib.rs

@@ -1,3 +1,5 @@
+#![allow(proc_macro_derive_resolution_fallback)] // This can be removed after diesel-1.4
+
 extern crate activitypub;
 extern crate ammonia;
 extern crate bcrypt;