git clone samza-hello-samza incorrect link

The page http://samza.apache.org/startup/hello-samza/0.8/
incorrectly states:

`git clone git://git.apache.org/samza-hello-samza.git hello-samza`

This misses the "apache" account on github and fails with:

```
➜ samza git clone git://git.apache.org/samza-hello-samza.git hello-samza
Cloning into 'hello-samza'...
fatal: unable to access 'https://git.apache.org/samza-hello-samza.git/': Failed connect to git.apache.org:443; Connection refused
```

What worked for me is in the apache account:

```
➜ samza git clone https://github.com/apache/samza-hello-samza.git
Cloning into 'samza-hello-samza'...
remote: Counting objects: 450, done.
remote: Total 450 (delta 0), reused 0 (delta 0), pack-reused 450
Receiving objects: 100% (450/450), 4.85 MiB | 1.78 MiB/s, done.
Resolving deltas: 100% (185/185), done.
Checking connectivity... done.
```