Make sure rustfmt is installed.

Jonathan Pallant (42 Technology) · Jonathan Pallant (42 Technology) · commit 697d87bb2404 · 2019-11-07T09:36:42.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -5,5 +5,6 @@ rust:
   - nightly
 install:
   - rustup target add thumbv7em-none-eabi thumbv7em-none-eabihf thumbv8m.main-none-eabi
+  - rustup component add rustfmt
 script:
   - scripts/build.sh
