Use regular expression to extract the SHA1 from the `git ls-remote` call
response. The reason is that there might be some messages in the
response going to stderr, that are captured when using run_command,
e.g.:
```
Could not chdir to home directory /home/johndoe: No such file or directory
fe87e2b75ed1850718d99c797cc171b88bfad5ca refs/tags/my-awesome-lib-1.0.1-1
```
I used 30 and more characters for the regular expression because I was
not sure the SHA1 is always shown as 40 characters. However we can be
quite certain that the word of 30 and more [0-9a-f] characters is a
SHA1.
