Fix copying of native libraries on osx

The suffix is "lib" for OSX (because that's what we have in the Maven package name). It's also the suffix for the native library files. Unfortunately the extensions are ".dylib" and ".jnilib".

Not requiring the dot when checking filenames is the less intrusive option for fixing this. (The other option I can see being: extend the lwjgl.os tuple with a new element: the list of extensions we want).