Switch to apple/swift-tools-support-core

… as opposed to using SwiftPM directly. This is way of the future.

Author: dduan

Package.swift

@@ -12,15 +12,15 @@ let package = Package(
       targets: ["FileCheck"]),
   ],
   dependencies: [
-    .package(url: "https://github.com/apple/swift-package-manager.git", from: "0.1.0"),
+    .package(url: "https://github.com/apple/swift-tools-support-core.git", .exact("0.0.1")),
     .package(url: "https://github.com/onevcat/Rainbow.git", from: "3.0.0"),
   ],
   targets: [
     .target(
       name: "FileCheck"),
     .target(
       name: "filecheck-tool",
-      dependencies: ["FileCheck", "SPMUtility", "Rainbow"]),
+      dependencies: ["FileCheck", "SwiftToolsSupport", "Rainbow"]),
     .testTarget(
       name: "FileCheckTests",
       dependencies: ["FileCheck"]),

Sources/filecheck-tool/main.swift

@@ -1,6 +1,6 @@
 import Foundation
-import Basic
-import SPMUtility
+import TSCBasic
+import TSCUtility
 import FileCheck
 import Rainbow