Mudanca de Estilo do HeroUnit

Mudei o main.css a parte do hero-unit.

```scss
.hero-unit {
  margin-bottom: 0;
  padding-bottom: 20px;
  background: url(../images/hero-bg.jpg) no-repeat center -100px fixed;
  @include background-size(cover);
  @include border-radius(0);
  
  iframe {
    max-width: 100%;
  }
  h1, p {
    color:#fff;
  }
}
```