add Stryker Mutator

according to https://stryker-mutator.io/stryker/quickstart (using npx)

with mutation testing limited to `lib/*.js`
(`lib/parser/pbxproj.js` not included)

and add generated Stryker artifacts to .gitignore

.gitignore

@@ -2,3 +2,5 @@ node_modules/*
 .DS_Store
 npm-debug.log
 package-lock.json
+.stryker-tmp
+reports

package.json

@@ -15,11 +15,15 @@
     "uuid": "^3.3.2"
   },
   "devDependencies": {
+    "@stryker-mutator/core": "^2.1.0",
+    "@stryker-mutator/html-reporter": "^2.1.0",
+    "@stryker-mutator/javascript-mutator": "^2.1.0",
     "nodeunit": "^0.11.3",
     "pegjs": "^0.10.0"
   },
   "scripts": {
     "pegjs": "node_modules/.bin/pegjs lib/parser/pbxproj.pegjs",
+    "stryker": "stryker run",
     "test": "node_modules/.bin/nodeunit test/parser test"
   },
   "license": "Apache-2.0",

stryker.conf.js

@@ -0,0 +1,11 @@
+module.exports = function(config) {
+  config.set({
+    mutator: "javascript",
+    mutate: [ 'lib/*.js' ],
+    packageManager: "npm",
+    reporters: ["html", "clear-text", "progress"],
+    testRunner: "command",
+    transpilers: [],
+    coverageAnalysis: "all"
+  });
+};