title: Update a submodule to the latest commit
body: <p>I have a project A which is a library and it is used in a project B.</p>
  
  <p>Both projects A and B have a separate repository on github BUT inside B we have a submodule of A.</p>
  
  <p>I edited some classes on the library, which is in the repo A, I pushed on the remote repo, so the library (repo A) is updated.</p>
  
  <p>These updates do not reflect on the "reference" (the submodule) the submodule refers to a previous commit.... what should I do in order to update the submodule on git?</p>