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.

src/routes/instance.rs

@@ -144,8 +144,8 @@ fn shared_inbox(conn: DbConn, data: String) -> String {
     match instance.received(&*conn, act) {
         Ok(_) => String::new(),
         Err(e) => {
-            println!("Shared inbox error: {}\n{}", e.cause(), e.backtrace());
-            format!("Error: {}", e.cause())
+            println!("Shared inbox error: {}\n{}", e.as_fail(), e.backtrace());
+            format!("Error: {}", e.as_fail())
         }
     }
 }