Added stryker to the project

stryker.conf.js

@@ -0,0 +1,17 @@
+module.exports = (config) => config.set({
+  mutate: [ 'src/**/*.js' ],
+  mutator: 'javascript',
+  testRunner: 'jest',
+  reporters: [ 'progress', 'clear-text', 'html' ],
+  coverageAnalysis: 'off',
+  jest: {
+    projectType: 'custom',
+    config: require(`${__dirname}/jest.config.js`),
+    enableFindRelatedTests: true,
+  },
+  thresholds: {
+    high: 80,
+    low: 60,
+    break: null,
+  },
+});