ISSUE-12 - Improved locale format handling to match RFC 5646

- Bumped Lingo dependency to 4.0.0

Package.swift

@@ -12,7 +12,7 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/vapor/vapor.git", from: "4.27.0"),
-        .package(url: "https://github.com/miroslavkovac/Lingo.git", from: "3.1.0")
+        .package(url: "https://github.com/miroslavkovac/Lingo.git", from: "4.0.0")
     ],
     targets: [
         .target(name: "LingoVapor", dependencies: [

README.md

@@ -14,13 +14,19 @@ Add LingoProvider as a dependancy in your `Package.swift` file:
 ```swift
 dependencies: [
 	...,
-	.package(name: "LingoVapor", url: "https://github.com/vapor-community/lingo-vapor.git", from: "4.0.0")]
+	.package(name: "LingoVapor", url: "https://github.com/vapor-community/lingo-vapor.git", from: "4.2.0")]
 ],
 targets: [
     .target(name: "App", dependencies: [
         .product(name: "LingoVapor", package: "LingoVapor")
 ```
 
+### Upgrading from version 4.1.0 to version 4.2.0
+
+The version 4.1.0 uses the new version of [Lingo](https://github.com/miroslavkovac/Lingo) where the format of locale identifiers was changed to match [RFC 5646](https://datatracker.ietf.org/doc/html/rfc5646). Prior to 4.2.0 `_` was used to separate _language code_ and _country code_ in the locale identifier, and now the library uses `-` as per RFC. 
+
+If you were using any locales which include a country code, you would need to rename related translation files to match the new format.    
+
 ### Add the Provider
 
 In the `configure.swift` simply initialize the `LingoVapor` with a default locale: