Strip out .err from our syntax highlighting styles because it fucks up our...

Strip out .err from our syntax highlighting styles because it fucks up our placeholders in code snippets

docs/assets/scss/_syntax.scss

 .hll { background-color: #ffc; }
 .c { color: #999; }
-.err { color: #a00; background-color: #faa; }
 .k { color: #069; }
 .o { color: #555; }
 .cm { color: #999; }