use terser and clean-css directly

create a sourcemap as well by default

node_modules/acorn/CHANGELOG.md

@@ -1,3 +1,39 @@
+## 6.4.0 (2019-11-26)
+
+### New features
+
+Add a static `acorn` property to the `Parser` class that contains the entire module interface, to allow plugins to access the instance of the library that they are acting on.
+
+## 6.3.0 (2019-08-12)
+
+### New features
+
+`sourceType: "module"` can now be used even when `ecmaVersion` is less than 6, to parse module-style code that otherwise conforms to an older standard.
+
+## 6.2.1 (2019-07-21)
+
+### Bug fixes
+
+Fix bug causing Acorn to treat some characters as identifier characters that shouldn't be treated as such.
+
+Fix issue where setting the `allowReserved` option to `"never"` allowed reserved words in some circumstances.
+
+## 6.2.0 (2019-07-04)
+
+### Bug fixes
+
+Improve valid assignment checking in `for`/`in` and `for`/`of` loops.
+
+Disallow binding `let` in patterns.
+
+### New features
+
+Support bigint syntax with `ecmaVersion` >= 10.
+
+Support dynamic `import` syntax with `ecmaVersion` >= 10.
+
+Upgrade to Unicode version 12.
+
 ## 6.1.1 (2019-02-27)
 
 ### Bug fixes