Precise sideEffects.

package.json

@@ -33,7 +33,10 @@
     "prepublishOnly": "rm -rf dist && yarn test",
     "postpublish": "git push && git push --tags && cd ../d3.github.com && git pull && cp ../${npm_package_name}/dist/${npm_package_name}.js ${npm_package_name}.v${npm_package_version%%.*}.js && cp ../${npm_package_name}/dist/${npm_package_name}.min.js ${npm_package_name}.v${npm_package_version%%.*}.min.js && git add ${npm_package_name}.v${npm_package_version%%.*}.js ${npm_package_name}.v${npm_package_version%%.*}.min.js && git commit -m \"${npm_package_name} ${npm_package_version}\" && git push && cd - && zip -j dist/${npm_package_name}.zip -- LICENSE README.md dist/${npm_package_name}.js dist/${npm_package_name}.min.js"
   },
-  "sideEffects": true,
+  "sideEffects": [
+    "./src/index.js",
+    "./src/selection/index.js"
+  ],
   "dependencies": {
     "d3-color": "1 - 2",
     "d3-dispatch": "1 - 2",