Plans for rust 1.26.x?

[Federico Mena Quintero <federico gnome org>]

Dear distributors,

For the development branch of librsvg (2.43.x), I'd like to increase
our Rust dependency to rustc 1.26.x.  It has some language and library
features that would make our life much easier.

Firefox 60, the long-term support release, will need Rust 1.26.x, so I
guess distros will be using that sooner or later.

Do you plan on using rustc 1.26.x any time soon?  The stable branch of
librsvg can still use older versions (it works with 1.21), but we'd
like to update the development branch as soon as possible.

Thanks!

  Federico