feat: update to uglify-es (#63)

Author: Hartorn

.eslintignore

@@ -3,4 +3,4 @@
 /dist
 /examples/build
 /coverage/
-/test/stubs
+/test/fixtures

package-lock.json

@@ -31,7 +31,7 @@
   },
   "dependencies": {
     "source-map": "^0.5.6",
-    "uglify-js": "^2.8.29",
+    "uglify-es": "^3.0.21",
     "webpack-sources": "^1.0.1"
   },
   "devDependencies": {
@@ -51,7 +51,6 @@
     "nsp": "^2.6.3",
     "pre-commit": "^1.2.2",
     "standard-version": "^4.1.0",
-    "uglify-js": "^2.8.18",
     "webpack": "^3.0.0",
     "webpack-defaults": "^1.4.0"
   },