title: Cypress "have.attr" with regular expressions
body: <p>In Cypress I can match an attribute's value by exact text like this:</p>
  
  <pre class="lang-js prettyprint-override"><code>cy.get("my-element")
    .should("have.attr", "title", "Exact title")
  </code></pre>
  
  <p>But, is there a way to match the attribute's value by a substring or a regular expression? something like:</p>
  
  <pre class="lang-js prettyprint-override"><code>cy.get("my-element")
    .should("have.attr", "title", /Partial title/)
  </code></pre>
  
  <p>So far, this is the best I have:</p>
  
  <pre class="lang-js prettyprint-override"><code>cy.get("my-element")
    .should("have.attr", "title")
    .then(title =&gt; expect(title).to.match(/Partial title/));
  </code></pre>