[fix] fix linting errors

src/fileExistsWithCaseSync.js

@@ -1,10 +1,10 @@
-var fs = require('fs');
-var path = require('path');
+const fs = require('fs');
+const path = require('path');
 
 // Based on https://stackoverflow.com/questions/27367261/check-if-file-exists-case-sensitive
 export default function fileExistsWithCaseSync(filepath) {
-    var dir = path.dirname(filepath);
-    if (dir === '/' || dir === '.') return true;
-    var filenames = fs.readdirSync(dir);
-    return filenames.indexOf(path.basename(filepath)) !== -1;
-}
+  const dir = path.dirname(filepath);
+  if (dir === '/' || dir === '.') return true;
+  const filenames = fs.readdirSync(dir);
+  return filenames.indexOf(path.basename(filepath)) !== -1;
+}

src/optimize.js

@@ -18,6 +18,7 @@ function validateAndFix(opts) {
       typeof opts.plugins === 'undefined' ||
       (Array.isArray(opts.plugins) && opts.plugins.length === 0)
     ) {
+      /* eslint no-param-reassign: 1 */
       opts.plugins = [...essentialPlugins];
       return;
     }
@@ -39,6 +40,7 @@ function validateAndFix(opts) {
           // make it essential
           if (!p[k]) p[k] = true;
           // and update state
+          /* eslint no-param-reassign: 1 */
           state[k] = true;
         }
       });