Add lint-staged

package.json

@@ -22,6 +22,7 @@
     "clean:src": "jlpm run clean",
     "clean:test": "lerna run clean --scope \"@jupyterlab/test-*\"",
     "clean:utils": "cd buildutils && jlpm run clean",
+    "precommit": "lint-staged",
     "coverage": "lerna run coverage --scope \"@jupyterlab/test-*\" --stream --concurrency 1",
     "create:package": "node buildutils/lib/create-package.js",
     "create:test": "node buildutils/lib/create-test-package.js",
@@ -53,7 +54,9 @@
     "eslint": "^4.12.1",
     "eslint-config-prettier": "^2.9.0",
     "eslint-plugin-prettier": "^2.6.0",
+    "husky": "^0.14.3",
     "lerna": "^2.4.0",
+    "lint-staged": "^7.1.0",
     "npm-run-all": "~4.1.1",
     "prettier": "^1.11.1",    
     "tslint": "~5.10.0",
@@ -61,6 +64,12 @@
     "tslint-plugin-prettier": "^1.3.0",
     "yarn": "1.6.0"
   },
+  "lint-staged": {
+    "**/*{.ts,.tsx,.js,.jsx,.css,.json,.md}": [
+      "prettier --write",
+      "git add"
+    ]
+  },
   "workspaces": [
     "dev_mode",
     "examples/*",