don't use cache while running PR builds

.travis.yml

@@ -12,7 +12,7 @@ before_install:
 install:
 - source ~/.cargo/env || true
 - cargo install mdbook --version '^0.4.3'
-- cargo install mdbook-linkcheck --version '^0.7.1'
+- cargo install mdbook-linkcheck --version '^0.7.2'
 script:
 - git checkout -b ci
 - git rebase origin/master

ci/linkcheck.sh

@@ -15,7 +15,7 @@ elif [ "$CI" = "true" ] ; then # running in PR CI build
   fi
 
   CHANGED_FILES=$(git diff --name-only $TRAVIS_COMMIT_RANGE | tr '\n' ' ')
-  FLAGS="-f $CHANGED_FILES"
+  FLAGS="--no-cache -f $CHANGED_FILES"
 
   echo "Checking files changed in $TRAVIS_COMMIT_RANGE: $CHANGED_FILES"
 else # running locally