Allow webpack 2 and 3 as peerDependencies

Despite the changes in webpack 2, this plugin is still needed in some instances (see for example the discussion here: TypeStrong/ts-loader#108).

Author: gabro

package.json

@@ -10,7 +10,7 @@
     "webpack"
   ],
   "peerDependencies": {
-    "webpack": "^1.9.11"
+    "webpack": "^1.9.11" || "^2" || "^3"
   },
   "author": "Tiddo Langerak <tiddolangerak@gmail.com>",
   "license": "MIT",