libraries - Only one file with GIT submodules -

from sorry if have spelling errors, english not good.

my problem/question easy:

i using git manage versions, , have use third-party libraries, gmaps.js example.

for example, if use:

$ git submodule add git://github.com/hpneo/gmaps.git webroot/javascripts 

in folder javascripts have files repository.

i need add 1 file: gmaps.js root of remote repository. , want update submodule, in fact want update file.

thank guys!