chore: Update CI

Author: epage

.travis.yml

@@ -11,22 +11,22 @@ os:
 matrix:
   include:
   - env: RUSTFMT
-    rust: 1.29.1  # `stable`: Locking down for consistent behavior
+    rust: 1.31.0  # `stable`: Locking down for consistent behavior
     install:
-      - rustup component add rustfmt-preview
+      - rustup component add rustfmt
     script:
       - cargo fmt -- --check
   - env: RUSTFLAGS="-D warnings"
-    rust: 1.29.1  # `stable`: Locking down for consistent behavior
+    rust: 1.31.0  # `stable`: Locking down for consistent behavior
     install:
     script:
     - cargo check --tests --all-features
   - env: CLIPPY
-    rust: nightly-2018-07-17
+    rust: 1.31.0  # `stable`: Locking down for consistent behavior
     install:
-      - rustup component add clippy-preview
+      - rustup component add clippy
     script:
-      - cargo clippy --all-features -- -D clippy
+      - cargo clippy --all-features
 
 install:
 - rustc -Vv