move uglify-js back to a peer-dep (fixes webpack-contrib#49)

Author: James Butler

package.json

@@ -42,11 +42,11 @@
   },
   "homepage": "https://github.com/webpack-contrib/uglifyjs-webpack-plugin",
   "peerDependencies": {
+    "uglify-js": "^2.8.0",
     "webpack": "^1.9 || ^2 || ^2.1.0-beta || ^2.2.0-rc || ^3.0.0"
   },
   "dependencies": {
     "source-map": "^0.5.6",
-    "uglify-js": "^2.8.29",
     "webpack-sources": "^1.0.1"
   },
   "devDependencies": {

yarn.lock

@@ -3655,7 +3655,7 @@ typedarray@^0.0.6:
   version "0.0.6"
   resolved "https://registry.npmjs.org/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
 
-uglify-js@^2.6, uglify-js@^2.8.27, uglify-js@^2.8.29:
+uglify-js@^2.6, uglify-js@^2.8.27:
   version "2.8.29"
   resolved "https://registry.npmjs.org/uglify-js/-/uglify-js-2.8.29.tgz#29c5733148057bb4e1f75df35b7a9cb72e6a59dd"
   dependencies: