title: Flutter SVG shows just one color
body: <p>I want to add <code>SVG</code> file in my project, and I used flutter_svg: ^0.17.3,
  my project shows the <code>SVG</code> but in fact, my <code>SVG</code> file has 2 colors but in the project, it shows just in one color!</p>
  <p>and source of svg file:</p>
  <pre><code>&lt;svg xmlns=&quot;http://www.w3.org/2000/svg&quot; viewBox=&quot;0 0 512 512&quot;&gt;
      &lt;defs&gt;
          &lt;style&gt;.fa-secondary{opacity:.4}&lt;/style&gt;
      &lt;/defs&gt;
      &lt;path d=&quot;M208 80a128 128 0 1 1-90.51 37.49A127.15 127.15 0 0 1 208 80m0-80C93.12 0 0 93.12 0 208s93.12 208 208 208 208-93.12 208-208S322.88 0 208 0z&quot; class=&quot;fa-secondary&quot;/&gt;&lt;path d=&quot;M504.9 476.7L476.6 505a23.9 23.9 0 0 1-33.9 0L343 405.3a24 24 0 0 1-7-17V372l36-36h16.3a24 24 0 0 1 17 7l99.7 99.7a24.11 24.11 0 0 1-.1 34z&quot; class=&quot;fa-primary&quot;/&gt;
  &lt;/svg&gt;
  </code></pre>