Add Rust version 1.25

[Majora320]

The current Rust version is from February, and, since Rust is a very fast-evolving language, lacks quite a few features available in current Rust. Please bump the version, and perhaps add additional tests; a test for the ? operator (introduced in 1.22) would probably be enough.

[kazk]

Rust v1.23.0 was added to the new system with following crates:

• rand
• num
• chrono
• regex
• text_io
• serde, serde_json

This will be made available when we switch to the new system. I'm not sure how soon that will be, but we'll start testing against real traffic soon.

[kazk]

Updated Rust to 1.25. We're planning to release it tonight.

[flip111]

In the dropdown box the 1.25 version is visible but not selectable and it's also not the default version.