fix(linkcheck): Build using the lockfile

This is to unblock cargo from servo/html5ever#623

Author: epage

src/tools/linkchecker/linkcheck.sh

@@ -98,6 +98,7 @@ then
     nightly_hash=$(rustc +nightly -Vv | grep commit-hash | cut -f2 -d" ")
     url="https://raw.githubusercontent.com/rust-lang/rust"
     mkdir linkchecker
+    curl -o linkchecker/Cargo.lock ${url}/${nightly_hash}/Cargo.lock
     curl -o linkchecker/Cargo.toml ${url}/${nightly_hash}/src/tools/linkchecker/Cargo.toml
     curl -o linkchecker/main.rs ${url}/${nightly_hash}/src/tools/linkchecker/main.rs
 fi