fix path

Author: heythisisnate

scripts/update-espwebtools-manifest.rb

@@ -13,4 +13,4 @@
 build = manifest['builds'].detect{|b| b['chipFamily'] == ENV['CHIP_FAMILY']}
 build['parts'] = { path: ENV['RELEASE_IMAGE_URI'], offset: 0 }
 puts manifest
-File.write('manifest.json', JSON.dump(manifest))
+File.write('assets/manifest.json', JSON.dump(manifest))