fix(rollup): npm requires an index.js file

Author: alexeagle

packages/rollup/src/BUILD.bazel

@@ -33,6 +33,7 @@ filegroup(
     srcs = [
         "BUILD.bazel",
         "index.bzl",
+        "index.js",
         "package.json",
         "rollup.config.js",
         "rollup_bundle.bzl",

packages/rollup/src/index.js

@@ -0,0 +1,9 @@
+// npm install throws if there is no JS in the package
+// npm ERR! path /home/alexeagle/Projects/angular/node_modules/@bazel/rollup/index.js
+// npm ERR! code ENOENT
+// npm ERR! errno -2
+// npm ERR! syscall chmod
+// npm ERR! enoent ENOENT: no such file or directory, chmod
+// '/home/alexeagle/Projects/angular/node_modules/@bazel/rollup/index.js' npm ERR! enoent This is
+// related to npm not being able to find a file. npm ERR! enoent
+throw new Error('@bazel/rollup package has no executable JS code');