add git command to alpine image

.gitlab-ci.yml

@@ -7,7 +7,7 @@ build_tagged_guide:
   image: alpine
   script:
     - apk update
-    - apk add ruby asciidoctor
+    - apk add ruby asciidoctor git
     - gem install asciidoctor-pdf --pre
     - export COMMIT_TIME=$(git show -s --format=%ci $CI_COMMIT_SHA | cut -c1-10)
     - asciidoctor-pdf -a revnumber=$CI_COMMIT_TAG -a revdate=$COMMIT_TIME -o angelguide_en.pdf guide.adoc
@@ -26,7 +26,7 @@ build_guide:
   image: alpine
   script:
     - apk update
-    - apk add ruby asciidoctor
+    - apk add ruby asciidoctor git
     - gem install asciidoctor-pdf --pre
     - export COMMIT_TIME=$(git show -s --format=%ci $CI_COMMIT_SHA | cut -c1-10)
     - echo $COMMIT_TIME