Workaround for builds.apache.org CI

The build on builds.apache.org fails due to the wrong nodejs binary being used.

Force usage of 64 bit binary.

<del>Until nodejs-maven-plugin is fixed (see https://github.com/skwakman/nodejs-maven-plugin/issues/8) don't use nodejs with the requirejs optimizer.</del>
Probably worth a comment explaining what it's for too.