Fix HTTP User-Agent sent by installer
Fix HTTP User-Agent sent by installer

The HTTP/1.1 spec mandates that the product identifier does not include
spaces, and that the version is separated from the product identifier by
a slash. See <https://tools.ietf.org/html/rfc7230#section-3.2.6>.

Fixes #166.

composer/getcomposer.org,composer/getcomposer.org,johnstevenson/getcomposer.org,johnstevenson/getcomposer.org,johnstevenson/getcomposer.org,composer/getcomposer.org