update the example of download from github hash

[agarcia]

As you are not using tags, I cant understand what commit is the actual release.

please change:

Alternatively, if you want to rely on an exact copy of the installer, you can fetch a specific version from GitHub's history. The commit hash should be enough to give it uniqueness and authenticity as long as you can trust the GitHub servers. For example:

wget https://raw.githubusercontent.com/composer/getcomposer.org/76a7060ccb93902cd7576b67264ad91c8a2700e2/web/installer -O - -q | php -- --quiet
You may replace the commit hash by whatever the last commit hash is on https://github.com/composer/getcomposer.org/commits/master

with the corresponding hash in release 1.9.1

I think is 7a00add3ad93349ef9eb502f268417f935250f22
but i am not sure

[Jordi Boggiano]

The installer file has nothing to do with the composer versions, and is not tagged at all. If you want to install a specific version of Composer, you can use something like:

wget https://raw.githubusercontent.com/composer/getcomposer.org/76a7060ccb93902cd7576b67264ad91c8a2700e2/web/installer -O - -q | php -- --quiet --version 1.9.1

Note the version added at the end.