Update default engines to > 0.25% (#1238)

Don’t use “last 2 versions”. See https://jamie.build/last-2-versions

src/utils/getTargetEngines.js

@@ -2,7 +2,7 @@ const browserslist = require('browserslist');
 const semver = require('semver');
 
 const DEFAULT_ENGINES = {
-  browsers: ['> 1%', 'last 2 versions', 'Firefox ESR'],
+  browsers: ['> 0.25%'],
   node: '6'
 };