Fix Travis build config

.travis.yml

@@ -16,14 +16,16 @@ matrix:
   allow_failures:
     - env: NAME='nightly'
     - env: NAME='kcov'
+
   include:
     - env: NAME='nightly'
       rust: nightly
+
     - env:
         - NAME='rustfmt'
         - PROTOBUF_CODEGEN_VERSION=2.0.0
         - PATH=$PATH:$HOME/.cargo/bin:$HOME/protobuf/bin
-      rust: nightly
+      rust: nightly-2018-07-22
       before_script:
         - rustup component add rustfmt-preview
         # Protoc plugin needed to generate proof.rs from proof.proto
@@ -36,6 +38,7 @@ matrix:
         - protoc --rust_out src/proto/ protobuf/proof.proto
       script:
         - cargo fmt --all -- --check
+
     - env: NAME='kcov'
       sudo: required # travis-ci/travis-ci#9061
       before_script:
@@ -45,7 +48,7 @@ matrix:
       script:
         - cargo kcov --print-install-kcov-sh | sh
         - cargo update # Creates `Cargo.lock` needed by next command
-        - cargo kcov --verbose --features dss --coveralls -- --verify --exclude-pattern=/.cargo,/usr/lib,src/proto
+        - cargo kcov --verbose --coveralls -- --verify --exclude-pattern=/.cargo,/usr/lib,src/proto
       addons:
         apt:
           packages:
@@ -54,13 +57,11 @@ matrix:
             - binutils-dev
             - libiberty-dev
             - zlib1g-dev 
-    - env:
-        - NAME='clippy'
-        # use env so updating versions causes cache invalidation
-        - CLIPPY_VERSION=0.0.200
-      rust: nightly-2018-05-14
+
+    - env: NAME='clippy'
+      rust: nightly-2018-07-22
       before_script:
-        - cargo install clippy --version $CLIPPY_VERSION || echo "clippy already installed"
+        - rustup component add clippy-preview
       script:
         - cargo clippy --all -- -D clippy