Update dependencies.

package.json

 {
   "name": "d3",
-  "version": "4.0.0-alpha.7",
+  "version": "4.0.0-alpha.8",
   "publishConfig": {
     "tag": "next"
   },
@@ -31,7 +31,7 @@
   },
   "devDependencies": {
     "faucet": "0.0",
-    "rollup": "0.24",
+    "rollup": "0.25",
     "rollup-plugin-json": "2",
     "rollup-plugin-npm": "1",
     "tape": "4",
@@ -53,11 +53,11 @@
     "d3-random": "0.2.0",
     "d3-request": "0.3.0",
     "d3-scale": "0.5.1",
-    "d3-selection": "0.6.0",
+    "d3-selection": "0.6.1",
     "d3-shape": "0.4.0",
     "d3-time": "0.2.0",
     "d3-time-format": "0.3.0",
     "d3-timer": "0.1.0",
-    "d3-voronoi": "0.2.1"
+    "d3-voronoi": "0.3.0"
   }
 }