Upgrade backend to Diesel 1.4

This commit upgrades Diesel, allowing us to re-enable some warnings and
has the nice benefit of consolidating (some) versions of `proc-macro2`,
`quote`, and `syn`.

Author: jtgeibel

Cargo.lock

@@ -47,7 +47,7 @@ htmlescape = "0.3.1"
 license-exprs = "^1.4"
 dotenv = "0.11.0"
 toml = "0.4"
-diesel = { version = "1.3.0", features = ["postgres", "serde_json", "chrono", "r2d2"] }
+diesel = { version = "1.4.0", features = ["postgres", "serde_json", "chrono", "r2d2"] }
 diesel_full_text_search = "1.0.0"
 diesel_ltree = "0.1.3"
 serde_json = "1.0.0"

Cargo.toml

@@ -1,5 +1,4 @@
 #![deny(warnings)]
-#![allow(unknown_lints, proc_macro_derive_resolution_fallback)] // This can be removed after diesel-1.4
 
 #[macro_use]
 extern crate diesel;

src/bin/update-downloads.rs

@@ -7,7 +7,6 @@
 #![deny(missing_debug_implementations, missing_copy_implementations)]
 #![deny(bare_trait_objects)]
 #![recursion_limit = "256"]
-#![allow(unknown_lints, proc_macro_derive_resolution_fallback)] // TODO: This can be removed after diesel-1.4
 
 #[macro_use]
 extern crate derive_deref;

src/lib.rs

@@ -1,5 +1,4 @@
 #![deny(warnings)]
-#![allow(unknown_lints, proc_macro_derive_resolution_fallback)] // TODO: This can be removed after diesel-1.4
 
 #[macro_use]
 extern crate diesel;