Update to rustfmt-preview (#348)

* Update to rustfmt-preview.

* Run "cargo fmt --all" with rustfmt 0.4.1.

rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.

* Fix a long line that rustfmt 0.4.1 can't handle.

* Remove unneeded commas left behind by rustfmt.

.travis.yml

@@ -16,7 +16,16 @@ addons:
 install:
     - pip3 install --user --upgrade mypy flake8
     - mypy --version
-    - travis_wait ./check-rustfmt.sh --install
+before_script:
+    - cargo uninstall rustfmt || true
+    - cargo install --list
+    - rustup toolchain install stable
+    - rustup component add --toolchain=stable rustfmt-preview
+    - rustup component list --toolchain=stable
+    - rustup show
+    - rustfmt +stable --version || echo fail
+    - rustup update
+    - rustfmt +stable --version
 script: ./test-all.sh
 cache:
     cargo: true