Precise sideEffects. (#115)

Author: mbostock

package.json

@@ -32,7 +32,10 @@
     "umd": "./dist/d3-transition.min.js",
     "default": "./src/index.js"
   },
-  "sideEffects": true,
+  "sideEffects": [
+    "./src/index.js",
+    "./src/selection/index.js"
+  ],
   "dependencies": {
     "d3-color": "1 - 3",
     "d3-dispatch": "1 - 3",