refactor: switch to swift 5

Author: kylef

.swift-version

@@ -1 +1 @@
-3.1
+5.0

.travis.yml

@@ -1,6 +1,6 @@
 language: objective-c
-osx_image: xcode8.3
+osx_image: xcode11.3
 install:
-  - eval "$(curl -sL https://gist.githubusercontent.com/kylef/5c0475ff02b7c7671d2a/raw/9f442512a46d7a2af7b850d65a7e9bd31edfb09b/swiftenv-install.sh)"
+  - eval "$(curl -sL https://swiftenv.fuller.li/install.sh)"
 script:
   - make build

Package.pins

@@ -1,10 +1,17 @@
+// swift-tools-version:4.0
 import PackageDescription
 
 
 let package = Package(
   name: "querykit",
+  products: [
+    .executable(name: "querykit", targets: ["querykit-cli"]),
+  ],
   dependencies: [
-    .Package(url: "https://github.com/kylef/Stencil.git", majorVersion: 0, minor: 9),
-    .Package(url: "https://github.com/kylef/Commander.git", majorVersion: 0, minor: 6),
+    .package(url: "https://github.com/kylef/Stencil.git", from: "0.9.0"),
+    .package(url: "https://github.com/kylef/Commander.git", from: "0.6.0"),
+  ],
+  targets: [
+    .target(name: "querykit-cli", dependencies: ["Stencil", "Commander"]),
   ]
 )