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/main.rs

@@ -1,4 +1,4 @@
-#![feature(custom_derive, decl_macro, plugin)]
+#![feature(custom_derive, plugin, decl_macro)]
 #![plugin(rocket_codegen)]
 
 extern crate activitypub;
@@ -13,6 +13,7 @@ extern crate heck;
 extern crate multipart;
 extern crate plume_common;
 extern crate plume_models;
+#[macro_use]
 extern crate rocket;
 extern crate rocket_contrib;
 extern crate rocket_csrf;