chore(examples): shorten if else statement (#11042)

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## Description
There is a statement which can be simplified to a simple single return statement.
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## Related Issues

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  Link to the issue that is fixed by this PR (if there is one)
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examples/gatsbygram/gatsby-browser.js

@@ -2,11 +2,7 @@ exports.shouldUpdateScroll = args => {
   const windowWidth = window.innerWidth
   // Scroll position only matters on mobile as on larger screens, we use a
   // modal.
-  if (windowWidth < 750) {
-    return true
-  } else {
-    return false
-  }
+  return windowWidth < 750
 }
 
 exports.onInitialClientRender = () => {