Install git for showcase-alternative-templates test case

Author: lidizheng

.circleci/config.yml

@@ -239,7 +239,7 @@ jobs:
           name: Install system dependencies.
           command: |
             apt-get update
-            apt-get install -y curl pandoc unzip
+            apt-get install -y curl pandoc unzip git
       - run:
           name: Install nox.
           command: pip install nox