Update to diesel v2

The changes are trivial:

* all methods now require a &mut reference to a Connection instance.
  Connections could not be shared between threads before, so all the
  references we had already were exclusive anyway

* begin_transaction() now calls the closure with one argument -- a &mut
  reference to the Connection instance

Author: malor

Cargo.lock

@@ -20,7 +20,7 @@ debug = true
 
 [dependencies]
 chrono = { version = "0.4.19", features = ["serde"] }
-diesel = { version = "1.4.5", features = ["chrono", "postgres", "r2d2"] }
+diesel = { version = "2.1.0", features = ["chrono", "postgres", "r2d2"] }
 jsonwebtoken = "7.2.0"
 rand = "0.7.3"
 reqwest = { version = "0.11.2", features = ["json"] }