title: Cargo build hangs with " Blocking waiting for file lock on the registry index" after building parity from source
body: <p>I followed the <a href="https://github.com/paritytech/parity#build-from-source" rel="noreferrer">readme</a> instructions for building <a href="https://www.parity.io/" rel="noreferrer">Parity</a> from source and then executed:</p>
  <pre class="lang-none prettyprint-override"><code>cargo build --release
  ~/.cargo/bin/cargo build --release
  </code></pre>
  <p>as instructed, both of which returned the following message while the prompt hung:</p>
  <pre><code> Blocking waiting for file lock on the registry index
  </code></pre>
  <p>I'm on a Mac.</p>