Use uglify-es until new terser gets published.

Author: goto-bus-stop

index.js

@@ -9,6 +9,7 @@ var uglifyify = require('uglifyify')
 
 function makeUglifyOptions (debug) {
   var uglifyOpts = {
+    uglify: require('uglify-es'),
     output: {
       ascii_only: true
     },

package.json

@@ -12,6 +12,7 @@
     "common-shakeify": "^0.4.6",
     "envify": "^4.1.0",
     "minify-stream": "^1.1.0",
+    "uglify-es": "^3.3.9",
     "uglifyify": "^5.0.0",
     "unassertify": "^2.1.1"
   },