title: Install rvm at a specific version
body: <p>According to the docs, I can specify the <code>--branch</code> option to point to an owner and branch when installing RVM. If I wanted to install specifically <code>1.25.15</code>, is there a way to do that? I see that versions are tagged on the git repo, so I could theoretically fork and checkout a branch at that tag and point to it. </p>
  
  <p>Is there a better way to do this?</p>
  
  <p>Keep in mind, I'm talking about the version of rvm, not the version of Ruby. </p>