Travis: add rustfmt and clippy components

Author: greyblake

.travis.yml

@@ -2,6 +2,9 @@ language: rust
 rust:
   - 1.30.1
   - stable
+install:
+  - rustup component add rustfmt-preview
+  - rustup component add clippy-preview
 script:
   - cargo fmt -- --check
   - cargo clippy -- -D warnings