rewrite `...` to `..=` as an idiom lint for Rust 2018 edition

**Current status**

Implemented in https://github.com/rust-lang/rust/pull/51149 but currently not marked as automatically applicable due to [this issue](https://github.com/rust-lang/rust/issues/51043#issuecomment-392252285) which is [explained below](https://github.com/rust-lang/rust/issues/51043#issuecomment-404390798)