Bump Package version to 4.0

Author: CodaFi

Package.swift

@@ -1,8 +1,15 @@
+// swift-tools-version:4.0
+
 import PackageDescription
 
 let package = Package(
   name: "LLVM",
+  products: [
+    .library(
+      name: "LLVM",
+      targets: ["LLVM"]),
+  ],
   dependencies: [
-    .Package(url: "https://github.com/trill-lang/cllvm.git", majorVersion: 0),
+    .package(url: "https://github.com/trill-lang/cllvm.git", .branch("master")),
   ]
 )