update circleci base docker image

Author: emmanueltouzery

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2
 jobs:
   build-lts:
     docker:
-      - image: fpco/stack-build:lts-11.11
+      - image: fpco/stack-build:lts-12.16
     steps:
       - checkout
       - restore_cache:
@@ -20,7 +20,7 @@ jobs:
 
   build-nightly:
     docker:
-      - image: fpco/stack-build:lts-11.11
+      - image: fpco/stack-build:lts-12.16
     steps:
       - checkout
       - restore_cache: