title: Font family set on Materia UI theme not working on browsers other than Chrome
body: <p>Need to override some elements with a specific font, which works fine on Chrome, but not any other browsers (Safari, FireFox, etc). Is there anything that was missed?</p>
  <p>Here is my code:</p>
  <pre class="lang-js prettyprint-override"><code>const theme = createMuiTheme({
          MuiTypography: {
              h1: {
                  fontFamily: 'Source Sans Pro'
              }
          }
      }
  });
  
  const MyApp = () =&gt; {
      return (
          &lt;ThemeProvider theme={theme}&gt;
              &lt;CssBaseline /&gt;
  
              &lt;Typography variant='h1'&gt;Source Sans Pro font applied on Chrome, but not on other browsers&lt;/Typography&gt;
          &lt;/ThemeProvider?
      )
  }
  </code></pre>