Update Autoprefixer and standardize browserlist location (#1899)

This updates Autoprefixer to 7.1.1, and also moves the browser target
list to package.json, in line with the recommendation made in this
article (https://evilmartians.com/chronicles/autoprefixer-7-browserslist-2-released)
from the developers of Autoprefixer and Browserslist.

resources/assets/build/config.js

@@ -25,7 +25,6 @@ const config = merge({
     watcher: !!argv.watch,
   },
   watch: [],
-  browsers: [],
 }, userConfig);
 
 module.exports = merge(config, {

resources/assets/build/webpack.config.js

@@ -141,7 +141,7 @@ let webpackConfig = {
         output: { path: config.paths.dist },
         context: config.paths.assets,
         postcss: [
-          autoprefixer({ browsers: config.browsers }),
+          autoprefixer(),
         ],
       },
     }),

resources/assets/build/webpack.config.optimize.js

@@ -13,7 +13,7 @@ module.exports = {
       cssProcessor: cssnano,
       cssProcessorOptions: {
         discardComments: { removeAll: true },
-        autoprefixer: { browsers: config.browsers },
+        autoprefixer: {},
       },
       canPrint: true,
     }),

resources/assets/config.json

@@ -14,10 +14,5 @@
   "cacheBusting": "[name]_[hash:8]",
   "watch": [
     "{app,resources/views}/**/*.php"
-  ],
-  "browsers": [
-    "last 2 versions",
-    "android 4",
-    "opera 12"
   ]
 }