Use Rust nightly, disable email notifications

.travis.yml

@@ -1,9 +1,13 @@
 language: rust
+rust:
+  - nightly
 cache: cargo
 before_script:
-- rustup component add rustfmt-preview
-- rustup target add x86_64-unknown-redox
+  - rustup component add rustfmt-preview
+  - rustup target add x86_64-unknown-redox
 script:
-- bash ./fmt.sh -- --write-mode=diff
-- bash ./test.sh
-- cargo build --target=x86_64-unknown-redox
+  - bash ./fmt.sh -- --write-mode=diff
+  - bash ./test.sh
+  - cargo build --target=x86_64-unknown-redox
+notifications:
+  email: false