Travis CI Build Failing : <p>I am having an issue with Travis CI - the commits that I push all fail with the same error:</p>

<blockquote>
  <p>0.06s$ curl -sSL "<a href="http://llvm.org/apt/llvm-snapshot.gpg.key">http://llvm.org/apt/llvm-snapshot.gpg.key</a>" | sudo -E apt-key add -
  gpg: no valid OpenPGP data found.
  The command "curl -sSL "<a href="http://llvm.org/apt/llvm-snapshot.gpg.key">http://llvm.org/apt/llvm-snapshot.gpg.key</a>" | sudo -E apt-key add -" failed and exited with 2 during .
  Your build has been stopped.</p>
</blockquote>

<p>I tried to rebuild a previous commit that built successfully and the same error occurs. Any suggestions as to how to troubleshoot the issue?</p>
