web-ext added to new devDependencies property in package.json

package.json

@@ -17,7 +17,9 @@
   },
   "homepage": "https://github.com/hamletv/image_a11y_extension#readme",
   "dependencies": {
-    "tesseract.js": "~1.0.10",
+    "tesseract.js": "~1.0.10"
+  },
+  "devDependencies": {
     "web-ext": "^2.8.0"
-  }
+  },
 }