build.sh generates broken builds when only one module is specified

e.g. `./build.sh -m twitter -l de` will spit errors and generate a build which is missing the twitter js and image files

This PR does fix this particular problem by not using brace extension when `$modules` contains only one module instead of a list of modules.

I'm not particularly happy with the solution but there are so many other things wrong (eval, ls instead of find, strings with filenames instead of proper arrays, ...) with the build script that the only other solution would have been rewriting the build script.