fix: window is not available during gatsby build

Check if window is available, and set initial value for `state.scrollY`.

src/components/HeaderBarebone/index.tsx

@@ -39,7 +39,6 @@ const BoxedTitle: React.FC<IBoxedTitleProps> = (props) => {
   )
 }
 
-
 const debounce = (fn) => {
   let frame
   return (...params) => {
@@ -57,13 +56,16 @@ export class HeaderBarebone extends Component<IHeaderBareboneProps, HeaderBarebo
   constructor(props) {
     super(props)
     this.tick = this.tick.bind(this)
+    this.state = { scrollY: 0 }
   }
 
   tick() {
+    if (typeof window !== 'undefined') {
       this.setState({
         scrollY: window.scrollY
       })
     }
+  }
 
   componentWillMount() {
     this.tick()