title: Undo a Mistake made while squashing the commits in GIT
body: <p>I wanted to squash my last 2 commits into one, so did a <code>git rebase</code>, in following way: </p>
  
  <pre><code>git rebase -i HEAD~2
  </code></pre>
  
  <p>but due to a typo, what I <strong>actually</strong> ended up pushing into origin was:</p>
  
  <pre><code>git rebase -i HEAD-3
  </code></pre>
  
  <p>Now, in the <a href="https://github.com/rails/rails/pull/5815#commits-pushed-06674f0" rel="noreferrer">Github Pull Request</a> it shows commit of some other unrelated commit. so basically, I want to remove commit <code>06674f0</code> which isn't mine, while keeping <code>fcea5e0</code> in this PR.</p>
  
  <p>how to fix the mess caused by simple typo?</p>