ci update

.travis.yml

@@ -107,7 +107,9 @@ before_install:
 
 
 install:
-  - cargo install cargo-travis || true
+  - cargo install cargo-update || echo "cargo-update already installed"
+  - cargo install cargo-travis || echo "cargo-travis already installed"
+  - cargo install-update -a # update outdated cached binaries
   - rustup override set nightly
   - rustup target add thumbv7m-none-eabi
   - rustup component add clippy-preview