Bumping LTS 11 to 11.20; config for LTS 12 (12.5)

Author: trskop

stack-lts-11.yaml

@@ -1,6 +1,6 @@
 # For advanced use and comprehensive documentation of the format, please see:
 # https://docs.haskellstack.org/en/stable/yaml_configuration/
-resolver: lts-11.5
+resolver: lts-11.20
 
 packages:
   - .

stack-lts-12.yaml

@@ -0,0 +1,10 @@
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+resolver: lts-12.5
+
+packages:
+  - .
+
+flags:
+  lock-file:
+    pedantic: true