Change indent for package.json from 2 to 4 spaces

Minor style issue more than anything.

If using `php artisan preset` it will use PHP's `JSON_PRETTY_PRINT` to rewrite the file (https://github.com/laravel/framework/blob/master/src/Illuminate/Foundation/Console/Presets/Preset.php#L44). `JSON_PRETTY_PRINT` uses four spaces for indentation, causing the entire file contents to be altered upon a diff.

Rather than adding logic to change the indentation after executing `json_encode()` in `Illuminate\Foundation\Console\Presets\Preset`, it seems easier to just fix the default indentation in `package.json`. NPM doesn't seem to change the spacing at all, so this seems like a happy medium.

package.json

@@ -1,21 +1,21 @@
 {
-  "private": true,
-  "scripts": {
-    "dev": "npm run development",
-    "development": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
-    "watch": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
-    "watch-poll": "npm run watch -- --watch-poll",
-    "hot": "cross-env NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
-    "prod": "npm run production",
-    "production": "cross-env NODE_ENV=production node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
-  },
-  "devDependencies": {
-    "axios": "^0.16.2",
-    "bootstrap-sass": "^3.3.7",
-    "cross-env": "^5.0.1",
-    "jquery": "^3.1.1",
-    "laravel-mix": "^1.0",
-    "lodash": "^4.17.4",
-    "vue": "^2.1.10"
-  }
+    "private": true,
+    "scripts": {
+        "dev": "npm run development",
+        "development": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
+        "watch": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
+        "watch-poll": "npm run watch -- --watch-poll",
+        "hot": "cross-env NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
+        "prod": "npm run production",
+        "production": "cross-env NODE_ENV=production node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
+    },
+    "devDependencies": {
+        "axios": "^0.16.2",
+        "bootstrap-sass": "^3.3.7",
+        "cross-env": "^5.0.1",
+        "jquery": "^3.1.1",
+        "laravel-mix": "^1.0",
+        "lodash": "^4.17.4",
+        "vue": "^2.1.10"
+    }
 }