move to cargo clippy instead of using the clippy plugin (#733)

* move to cargo clippy instead of using the clippy plugin

fixes #729

* non-exectable scripts must be run with `sh`

* don't build serde in the clippy travis job

* only run clippy tests if installing clippy succeeds

* why is travis so picky?

* no more serde_codegen

* serde_test_suite_deps has no features

* don't use empty loops, llvm optimizes them to undefined behaviour

* abort the clippy job when clippy lints are triggered

* use caches on travis to speed up builds

* why are we even using `travis-cargo`?

* need to reinstall clippy frequently due to nightly updates

* command line tools are hard

.travis.yml

@@ -1,5 +1,6 @@
 sudo: false
 language: rust
+cache: cargo
 
 # run builds for all the trains (and more)
 rust:
@@ -8,20 +9,16 @@ rust:
   - beta
   - nightly
 
+matrix:
+  include:
+    - rust: nightly
+      env: CLIPPY=true
+
 before_script:
   - pip install 'travis-cargo<0.2' --user
   - export PATH=$HOME/.local/bin:$PATH
 
-script:
-  - (cd serde && travis-cargo build)
-  - (cd serde && travis-cargo --only beta test)
-  - (cd serde && travis-cargo --only nightly test -- --features unstable-testing)
-  - (cd serde && travis-cargo build -- --no-default-features)
-  - (cd serde && travis-cargo --only nightly build -- --no-default-features --features alloc)
-  - (cd serde && travis-cargo --only nightly build -- --no-default-features --features collections)
-  - (cd test_suite && travis-cargo --only beta test)
-  - (cd test_suite/deps && travis-cargo --only nightly build && cd .. && travis-cargo --only nightly test -- --features unstable-testing)
-  - (cd test_suite/no_std && travis-cargo --only nightly build)
+script: sh travis.sh
 
 env:
   global: