clippy fallback

Signed-off-by: Yoshua Wuyts <[email protected]>

Author: yoshuawuyts

.travis.yml

@@ -3,8 +3,15 @@ rust:
   - nightly
 
 before_script: |
-  rustup component add rustfmt-preview;
   rustup component add clippy-preview;
+  if ! rustup component add clippy; then
+    target=`curl https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/clippy`;
+    echo "'clippy' is unavailable on the toolchain 'nightly', using the toolchain 'nightly-$target' instead";
+    rustup toolchain install nightly-$target;
+    rustup default nightly-$target;
+    rustup component add clippy;
+  fi
+  rustup component add rustfmt-preview;
   if ! rustup component add rustfmt; then
     target=`curl https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/rustfmt`;
     echo "'rustfmt' is unavailable on the toolchain 'nightly', use the toolchain 'nightly-$target' instead";