Run the linter on the minimum supported rust version; otherwise we will
get lint warnings for things that require a too high Rust toolchain
version to fix.
Allow the following checks, since we already violate them our code:
- clippy::new-without-default
- clippy::match-bool
- clippy::if_same_then_else
Eventually we should fix these lint issues and then disallow them to
prevent them from coming back in other places.
The clippy args used is recommended here:
https://github.com/rust-lang/rust-clippy#travis-ci
Martin Nordholts
28f3f3c9c9