add prettier

.prettierrc

@@ -0,0 +1,15 @@
+{
+  "printWidth": 100,
+  "singleQuote": true,
+  "trailingComma": "es5",
+  "useTabs": true,
+  "proseWrap": false,
+  "overrides": [{
+    "files": "*.md",
+    "options": {
+      "printWidth": 70,
+      "useTabs": false,
+      "trailingComma": "none"
+    }
+  }]
+}

package.json

@@ -119,7 +119,7 @@
     "jest": "^21.2.1",
     "keymirror": "^0.1.1",
     "lint-staged": "^4.3.0",
-    "prettier": "~1.8.1",
+    "prettier": "^1.8.2",
     "raf": "^3.4.0",
     "react": "^16.0.0",
     "react-dom": "^16.0.0",
@@ -132,7 +132,7 @@
   },
   "scripts": {
     "pretest": "npm run lint",
-    "test": "npm run test:jest",
+    "test": "npm run test:jest && npm run format:md",
     "test:jest": "jest",
     "test:watch": "jest --watch",
     "test:coverage": "jest --coverage",
@@ -154,7 +154,8 @@
     "test:browser:customised": "node test/browser.js examples/customised/styleguide/index.html",
     "test:browser:sections": "node test/browser.js examples/sections/styleguide/index.html",
     "danger": "danger",
-    "precommit": "lint-staged"
+    "precommit": "lint-staged",
+    "format:md": "prettier --write '**/*.md'"
   },
   "release": {
     "analyzeCommits": "semantic-release-tamia/analyzeCommits",