Switch to yarn. Update jest (microsoft#10)

* Switch to yarn

* Update jest

Author: Xapphire13

jest.config.js

@@ -0,0 +1,28 @@
+module.exports = {
+  clearMocks: true,
+  coverageDirectory: "coverage",
+  collectCoverageFrom: [
+    "src/**/*.ts",
+    "tests/**/*.ts"
+  ],
+  coveragePathIgnorePatterns: [
+    "/node_modules/",
+    "types.ts"
+  ],
+  globals: {
+    "ts-jest": {
+      tsConfigFile: "tests/tsconfig.json",
+      skipBabel: true
+    }
+  },
+  moduleFileExtensions: [
+    "ts",
+    "tsx",
+    "js"
+  ],
+  testEnvironment: "node",
+  testRegex: "/tests/.*\\.test\\.tsx?$",
+  transform: {
+    "^.+\\.tsx?$": "ts-jest"
+  }
+};