The following additional plugins were being used because of our use of
the older version of Uglify:
```
Using plugins:
check-es2015-constants {"uglify":true}
transform-es2015-arrow-functions {"uglify":true}
transform-es2015-block-scoped-functions {"uglify":true}
transform-es2015-block-scoping {"uglify":true}
transform-es2015-classes {"uglify":true}
transform-es2015-computed-properties {"uglify":true}
transform-es2015-duplicate-keys {"uglify":true}
transform-es2015-for-of {"uglify":true}
transform-es2015-literals {"uglify":true}
transform-es2015-object-super {"uglify":true}
transform-es2015-parameters {"uglify":true}
transform-es2015-shorthand-properties {"uglify":true}
transform-es2015-spread {"uglify":true}
transform-es2015-sticky-regex {"uglify":true}
transform-es2015-template-literals {"uglify":true}
transform-es2015-typeof-symbol {"uglify":true}
transform-es2015-unicode-regex {"uglify":true}
transform-regenerator {"uglify":true}
transform-exponentiation-operator {"uglify":true}
transform-async-to-generator {"uglify":true}
syntax-trailing-function-commas {"uglify":true}
```
