Add lint for src

package.json

@@ -6,7 +6,8 @@
   "scripts": {
     "start": "concurrently --kill-others \"watchify src/index.js  -t [ envify --NODE_ENV development ] -t [ babelify --presets [ es2015 ] ] -o dist/tesseract.dev.js --standalone Tesseract\" \"watchify src/browser/worker.js  -t [ envify --NODE_ENV development ] -t [ babelify --presets [ es2015 ] ] -o dist/worker.dev.js\" \"http-server -p 7355\"",
     "build": "browserify src/index.js -t [ babelify --presets [ es2015 ] ] -o dist/tesseract.js --standalone Tesseract && browserify src/browser/worker.js -t [ babelify --presets [ es2015 ] ] -o dist/worker.js && uglifyjs dist/tesseract.js --source-map -o dist/tesseract.min.js && uglifyjs dist/worker.js --source-map -o dist/worker.min.js",
-    "release": "npm run build && git commit -am 'new release' && git push && git tag `jq -r '.version' package.json` && git push origin --tags && npm publish"
+    "release": "npm run build && git commit -am 'new release' && git push && git tag `jq -r '.version' package.json` && git push origin --tags && npm publish",
+    "lint": "eslint src"
   },
   "browser": {
     "./src/node/index.js": "./src/browser/index.js"