Avoid possibility of adding config/private.yml

`git add --all` is too heavy handed a command. It is better to not rely
on the `.gitignore`.

[#169054090](https://www.pivotaltracker.com/story/show/169054090)

Author: bwasmith

ci/tasks/bump-cli-release.yml

@@ -50,7 +50,7 @@ run:
       bosh add-blob ../cli-binary-linux-64/cf-cli_${LATEST_CLI_VERSION}_linux_x86-64.tgz cf-cli_${LATEST_CLI_VERSION}_linux_x86-64.tgz
       bosh upload-blobs
 
-      git add --all
+      git add config/blobs.yml
       git status
       git commit -m "bump cli to ${LATEST_CLI_VERSION}"
     else