fix(useMutation): revert uneeded changes

Author: raoufswe

src/react/useMutation.ts

@@ -99,7 +99,7 @@ export function useMutation<
   const mutate = React.useCallback<
     UseMutateFunction<TData, TError, TVariables, TContext>
   >((variables, mutateOptions) => {
-    return obsRef.current!.mutate(variables, mutateOptions).catch(noop)
+    obsRef.current!.mutate(variables, mutateOptions).catch(noop)
   }, [])
 
   if (currentResult.error && obsRef.current.options.useErrorBoundary) {