Use servant-prometheus branch with complying metric names

stack.yaml

@@ -42,7 +42,7 @@ extra-deps:
   - "stripe-haskell-2.5.0"
   - "stripe-http-client-2.5.0"
   - github: "PrivateStorageio/servant-prometheus"
-    commit: "ec21c5ed50e6f6f8e52916ce71cd68fcd0166cad"
+    commit: "b1207d687aeb48bd035f986e88287391e4937e23"
 
 # Override default flag values for local packages and extra-deps
 # flags: {}