chore: add prettier

Author: vltansky

.prettierrc

@@ -0,0 +1,6 @@
+{
+    "printWidth": 120,
+    "trailingComma": "es5",
+    "singleQuote": true,
+    "useTabs": true
+  }

package-lock.json

@@ -19,6 +19,7 @@
   },
   "scripts": {
     "test": "jest",
+    "format": "prettier --write \"./cli.js\"",
     "coverage": "jest --coverage --collectCoverageOnlyFrom ./cli.js",
     "start": "node ./index.js ./out"
   },
@@ -31,6 +32,7 @@
     "yargs-parser": "^18.1.3"
   },
   "devDependencies": {
-    "jest": "^26.0.1"
+    "jest": "^26.0.1",
+    "prettier": "^2.0.5"
   }
 }