Swift package update (#68)

Update Publish’s dependencies to their latest versions:

- Ink `0.4.0`
- Plot `0.6.0`
- Sweep `0.4.0`

Also use Sweep’s new `firstSubstring` API.

Author: JohnSundell

Package.resolved

@@ -20,7 +20,7 @@ let package = Package(
         .package(url: "https://github.com/johnsundell/files.git", from: "4.0.0"),
         .package(url: "https://github.com/johnsundell/codextended.git", from: "0.1.0"),
         .package(url: "https://github.com/johnsundell/shellout.git", from: "2.3.0"),
-        .package(url: "https://github.com/johnsundell/sweep.git", from: "0.3.0")
+        .package(url: "https://github.com/johnsundell/sweep.git", from: "0.4.0")
     ],
     targets: [
         .target(

Package.swift

@@ -33,7 +33,7 @@ final class RSSFeedGenerationTests: PublishTestCase {
         ])
 
         let feed = try folder.file(at: "Output/feed.rss").readAsString()
-        let substring = feed.substrings(between: "BEGIN ", and: " END").first
+        let substring = feed.firstSubstring(between: "BEGIN ", and: " END")
 
         XCTAssertEqual(substring, """
         <a href="https://swiftbysundell.com/page">Link</a> \