uglify-es: update repository and project tagline (#2221)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "uglify-es",
-  "description": "JavaScript parser, mangler/compressor and beautifier toolkit",
+  "description": "JavaScript parser, mangler/compressor and beautifier toolkit for ES6+",
   "homepage": "https://github.com/mishoo/UglifyJS2/tree/harmony",
   "author": "Mihai Bazon <mihai.bazon@gmail.com> (http://lisperator.net/)",
   "license": "BSD-2-Clause",
@@ -11,7 +11,7 @@
   "maintainers": [
     "Mihai Bazon <mihai.bazon@gmail.com> (http://lisperator.net/)"
   ],
-  "repository": "https://github.com/mishoo/UglifyJS2/tree/harmony",
+  "repository": "git+https://github.com/mishoo/UglifyJS2.git#harmony",
   "bugs": {
     "url": "https://github.com/mishoo/UglifyJS2/issues"
   },
@@ -39,12 +39,16 @@
   },
   "keywords": [
     "uglify",
-    "uglify-js",
     "uglify-es",
+    "uglify-js",
     "minify",
     "minifier",
+    "javascript",
+    "ecmascript",
     "es5",
     "es6",
+    "es7",
+    "es8",
     "es2015",
     "es2016",
     "es2017",