fix: change react-dnd from dependency to peerDependency

Fixes #9

Author: Dang Hai An

package.json

@@ -28,8 +28,8 @@
     "url": "https://github.com/zyzo/react-dnd-mouse-backend/issues"
   },
   "homepage": "https://github.com/zyzo/react-dnd-mouse-backend#readme",
-  "dependencies": {
-    "react-dnd": "^2.1.2"
+  "peerDependencies": {
+    "react-dnd": ">=2.1.2"
   },
   "devDependencies": {
     "babel": "^6.5.2",