Use exact paths in imports. d3/d3#3265

Author: mbostock

src/axis.js

@@ -1,5 +1,5 @@
-import {slice} from "./array";
-import identity from "./identity";
+import {slice} from "./array.js";
+import identity from "./identity.js";
 
 var top = 1,
     right = 2,

src/index.js

@@ -3,4 +3,4 @@ export {
   axisRight,
   axisBottom,
   axisLeft
-} from "./axis";
+} from "./axis.js";