cargo-deadlinks: ignore fragments

These caused failures (see #1072)

.travis.yml

@@ -38,8 +38,7 @@ matrix:
         - bash utils/ci/script.sh
         # remove cached documentation, otherwise files from previous PRs can get included
         - rm -rf target/doc
-        - cargo doc --no-deps --all --all-features
-        - cargo deadlinks --dir target/doc
+        - cargo deadlinks --ignore-fragments -- --all-features --all
       deploy:
         local_dir: target/doc
         provider: pages