[openspending,stories][xs]: update file references to point to storage and add authors

examples/openspending/content/stories/frankfurt-is-investing-in-education-and-your-city-should-too.mdx

@@ -1,6 +1,7 @@
 ---
 title: Frankfurt is Investing in Education, and Your City Should Too
 date: 06/12/2023
+authors: ['Michael Polidori']
 ---
 
 _Note: The currency in this post has been converted to USD using an average exchange rate of 1 EUR = 1.20 USD._
@@ -18,7 +19,7 @@ The city's commitment to education is abundantly clear.
   spec={{
     $schema: 'https://vega.github.io/schema/vega-lite/v5.json',
     data: {
-      url: 'https://gist.githubusercontent.com/mpolidori/59ba986bc82379191fe48faa446f5110/raw/d3863c5c958d99db43207b13abf8896d88b2e879/frankfurt-sums.csv',
+      url: 'https://storage.openspending.org/city-of-frankfurt-expenditure/frankfurt-sums.csv',
     },
     transform: [
       {
@@ -120,7 +121,7 @@ the key to a prosperous future.
     $schema: 'https://vega.github.io/schema/vega-lite/v5.json',
     description: 'Frankfurt Education Spending.',
     data: {
-      url: 'https://gist.githubusercontent.com/mpolidori/59ba986bc82379191fe48faa446f5110/raw/d3863c5c958d99db43207b13abf8896d88b2e879/frankfurt-sums.csv',
+      url: 'https://storage.openspending.org/city-of-frankfurt-expenditure/frankfurt-sums.csv',
     },
     transform: [
       { filter: "datum.label==='Education'" },