Update Travis configuration

Silence emails on successful builds, don't be verbose. Fixes #6

.travis.yml

@@ -16,7 +16,7 @@ matrix:
     - name: "Clippy"
       rust: stable
       before_script: rustup component add clippy-preview
-      script: cargo clippy --all
+      script: cargo clippy
 
     - name: "rustfmt"
       rust: stable
@@ -30,15 +30,19 @@ matrix:
     - name: "release"
       rust: stable
       script:
-        - cargo build --verbose --all --release
-        - cargo test --verbose --all --release
-        - cargo doc --verbose --all --release
+        - cargo build --release
+        - cargo test --release
+        - cargo doc --release
 
     - os: osx
       osx_image: xcode10
     - os: windows
 
 script:
-- cargo build --all --verbose
-- cargo test --all --verbose
-- cargo doc --all --verbose
+- cargo build
+- cargo test
+- cargo doc
+
+notifications:
+  email:
+    on_success: never