[sr.ht] Change build to nix flakes

.builds/build.yml

@@ -1,13 +1,11 @@
-image: freebsd
+image: nixos/unstable
-packages:
-  - stack
-  - ghc
 sources:
   - https://git.sr.ht/~dbalan/blogng
 tasks:
   - build: |
-      uname -a
       cd blogng
-      echo "I AM BROKEN"
+      nix build
-      #stack build
+triggers:
-      #stack exec site build
+  - action: email
+    condition: failure
+    to: "Build Logs <build@dbalan.in>"