Try to read lastmod from git details

It's better than just assuming it never changes

.gitlab-ci.yml

@@ -27,7 +27,7 @@ build:
   image: node:alpine
   stage: build
   before_script:
-    - apk add --no-cache hugo
+    - apk add --no-cache hugo git
   script:
     - ./scripts/release.sh
   artifacts:

config.yml

@@ -25,6 +25,8 @@ enableEmoji: true
 MetaDataFormat: yaml
 stepAnalysis: true
 
+enableGitInfo: true
+
 pygmentsCodefencesGuessSyntax: true
 pygmentsCodefences: true
 pygmentsUseClasses: true