Update travis CI script

Build only on latest Rust stable. That simplifies the build script,
removes MaidSafe installation scripts, etc.

.travis.yml

@@ -2,37 +2,24 @@ env:
   global:
     - RUST_BACKTRACE=1
     - PATH=$PATH:$HOME/.cargo/bin
-    - RUST_STABLE=1.26.2
-    - RUST_NIGHTLY=nightly-2018-06-10
-    - RUST_CLIPPY=0.0.207
 os:
   - linux
 language: rust
-rust:
-  - 1.26.2
-  - nightly-2018-06-10
 sudo: false
 cache:
   cargo: true
 before_script:
   - sudo apt-get update
   - sudo apt-get install -y libcap-dev
-  - curl -sSL https://github.com/maidsafe/QA/raw/master/travis/cargo_install.sh > cargo_install.sh
-  - bash cargo_install.sh cargo-prune;
-    if [ "$TRAVIS_RUST_VERSION" = "$RUST_NIGHTLY" ] && [ "$TRAVIS_OS_NAME" = linux ]; then
-      bash cargo_install.sh clippy "$RUST_CLIPPY";
+  - if ! cargo prune --version | grep -q "0.1.8"; then
+      cargo install cargo-prune --vers="0.1.8" --force;
     fi
+  - rustup component add clippy
 script:
-  - if [ "$TRAVIS_RUST_VERSION" = "$RUST_STABLE" ]; then
-      (
-        set -x;
-        cargo test --release --verbose --no-default-features
-      );
-    elif [ "$TRAVIS_OS_NAME" = linux ]; then
-      (
-        set -x;
-        cargo clippy --profile=test
-      );
+  - set -x;
+    cargo test --release --verbose --no-default-features
+  - if [ "${TRAVIS_OS_NAME}" = linux ]; then
+      cargo clippy --verbose --release --all-targets ;
     fi
   - cargo check --examples
 before_cache: