Add back IE11 temporarily to our targets

- In recent Browserslist version the "not dead" query removes IE11.
This breaks our ES5 check on the legacy bundle.
Add it back temporarily, until we tackle the major Babel/targets etc
revamp.

index.js

@@ -30,7 +30,13 @@ module.exports = (context, options = {}) => {
   let envOpts = Object.assign(
     {
       targets: {
-        browsers: ['last 2 versions', '> 1%', 'Firefox ESR', 'not dead'],
+        browsers: [
+          'last 2 versions',
+          '> 1%',
+          'not dead',
+          'Firefox ESR',
+          'IE 11',
+        ],
       },
       bugfixes: options.targets && options.targets.esmodules === true,
     },