Ignore git directory in .dockerignore

This will prevent docker images getting slower to build as the git history grows

.dockerignore

@@ -1,8 +1,11 @@
 # See https://docs.docker.com/engine/reference/builder/#dockerignore-file
 # Put files here that you don't want copied into your bundle's invocation image
-.gitignore
 Dockerfile.tmpl
 
+# Ignore git directories
+.git
+.gitignore
+
 vitess/**
 
 !vitess/examples/operator/operator.yaml