Turn revision file to history of revision

to_pdf.js

@@ -67,7 +67,7 @@ function writeGitRevisionFile(dataFilePath, templatePath, assetsPath, revPath) {
       return;
     }
 
-    fs.writeFile(revPath, stdout, (err) => {
+    fs.appendFile(revPath, stdout, (err) => {
       if (err) throw err;
     });
     console.log(`Wrote file revision data to ${revPath}`);