stack.yaml.lock: Add stack lock file

stack.yaml.lock

@@ -0,0 +1,12 @@
+# This file was autogenerated by Stack.
+# You should not edit this file by hand.
+# For more information, please see the documentation at:
+#   https://docs.haskellstack.org/en/stable/lock_files
+
+packages: []
+snapshots:
+- completed:
+    size: 499178
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/12/0.yaml
+    sha256: 3e9a7b96708cd9196ce7e5396143725097a71f2e9ca8dc19f03f5082642bc1b5
+  original: lts-12.0