fix: add server check back for rAF (#899)

Author: joakimgrr

src/use-swr.ts

@@ -577,7 +577,7 @@ function useSWR<Data = any, Error = any>(
       config.revalidateOnMount ||
       (!config.initialData && config.revalidateOnMount === undefined)
     ) {
-      if (typeof latestKeyedData !== 'undefined') {
+      if (typeof latestKeyedData !== 'undefined' && !IS_SERVER) {
         // delay revalidate if there's cache
         // to not block the rendering
         rAF(softRevalidate)