Library::version can return multiple lines

[bmatcuk]

When using version number restrictions (such as atleast_version), the resulting pkg-config command will return the version number multiple times on different lines. For example, I have the following in my code:

    let libuv = pkg_config::Config::new()
        .range_version("1.30".."1.31")
        .probe("libuv");

Which results in something like the following getting run:

$ pkg-config --modversion libuv 'libuv >= 1.30' 'libuv < 1.31'
1.30.1
1.30.1
1.30.1

So libuv.version ends up being a string with the version repeated three times on different lines.