Build dependencies first with a longer no-output timeout

try to get around the timeout problem on slow CircleCI builders

.circleci/config.yml

@@ -74,6 +74,15 @@ jobs:
             - paymentserver-v1-{{ checksum "stack.yaml" }}-{{ checksum "PaymentServer.cabal" }}
             - paymentserver-v1-{{ checksum "stack.yaml" }}
 
+      - run:
+          name: "Build Dependencies"
+          command: |
+            nix-shell shell.nix --run "stack build --only-dependencies --interleaved-output"
+
+          # Give it a good long while.  stripe-core, in particular, can take a
+          # while to build.
+          no_output_timeout: "20m"
+
       - run:
           name: "Run Tests"
           command: |