Update Leaf docs (#991)

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<!-- Describe your changes clearly and use examples if possible. -->
Update Leaf docs to accept time zone IDs as argument in `#date` tag

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docs/leaf/getting-started.it.md

@@ -7,7 +7,7 @@ Leaf è un potente linguaggio di templating con la sintassi ispirata a Swift. Pu
 Il primo passo per usare Leaf è aggiungerlo come una dipendenza al tuo progetto nel tuo file di manifesto del pacchetto SPM.
 
 ```swift
-// swift-tools-version:5.2
+// swift-tools-version:5.8
 import PackageDescription
 
 let package = Package(
@@ -17,7 +17,7 @@ let package = Package(
     ],
     dependencies: [
         /// Qualsiasi altra dipendenza ...
-        .package(url: "https://github.com/vapor/leaf.git", from: "4.0.0"),
+        .package(url: "https://github.com/vapor/leaf.git", from: "4.4.0"),
     ],
     targets: [
         .target(name: "App", dependencies: [

docs/leaf/getting-started.md

@@ -7,7 +7,7 @@ Leaf is a powerful templating language with Swift-inspired syntax. You can use i
 The first step to using Leaf is adding it as a dependency to your project in your SPM package manifest file.
 
 ```swift
-// swift-tools-version:5.2
+// swift-tools-version:5.8
 import PackageDescription
 
 let package = Package(
@@ -17,7 +17,7 @@ let package = Package(
     ],
     dependencies: [
         /// Any other dependencies ...
-        .package(url: "https://github.com/vapor/leaf.git", from: "4.0.0"),
+        .package(url: "https://github.com/vapor/leaf.git", from: "4.4.0"),
     ],
     targets: [
         .target(name: "App", dependencies: [

docs/leaf/overview.it.md

@@ -264,6 +264,12 @@ Puoi passare una stringa in un formato di data personalizzato come secondo argom
 The date is #date(now, "yyyy-MM-dd")
 ```
 
+Puoi anche passare l'ID di un fuso orario come terzo argomento. Guarda [`DateFormatter.timeZone`](https://developer.apple.com/documentation/foundation/dateformatter/1411406-timezone) e [`TimeZone`](https://developer.apple.com/documentation/foundation/timezone) di Swift per più informazioni.
+
+```leaf
+The date is #date(now, "yyyy-MM-dd", "America/New_York")
+```
+
 #### `#unsafeHTML`
 
 Il tag `#unsafeHTML` agisce come un tag di variabile - p.es. `#(variable)`. Però non evade nessun HTML che `variable` potrebbe contenere:

docs/leaf/overview.md

@@ -264,6 +264,12 @@ You can pass a custom date formatter string as the second argument. See Swift's
 The date is #date(now, "yyyy-MM-dd")
 ```
 
+You can also pass a time zone ID for the date formatter as the third argument. See Swift's [`DateFormatter.timeZone`](https://developer.apple.com/documentation/foundation/dateformatter/1411406-timezone) and [`TimeZone`](https://developer.apple.com/documentation/foundation/timezone) for more information.
+
+```leaf
+The date is #date(now, "yyyy-MM-dd", "America/New_York")
+```
+
 #### `#unsafeHTML`
 
 The `#unsafeHTML` tag acts like a variable tag - e.g. `#(variable)`. However it does not escape any HTML that `variable` may contain: