Specify git revision to avoid breakage as possible on semverver

.github/workflows/bors.yml

@@ -234,7 +234,7 @@ jobs:
           github_token: "${{ secrets.GITHUB_TOKEN }}"
       - uses: actions/checkout@v2
       - name: Setup Rust toolchain
-        # FIXME: Pin nightly version to make semverver compilable.
+        # Should update the semverver revision in semver.sh if we touch nightly ver.
         run: TOOLCHAIN=nightly-2020-11-19 sh ./ci/install-rust.sh
       - name: Check breaking changes
         run: sh ci/semver.sh linux

ci/semver.sh

@@ -15,7 +15,8 @@ fi
 
 rustup component add rustc-dev llvm-tools-preview
 
-cargo install --git https://github.com/rust-dev-tools/rust-semverver
+# Should update the nightly version in bors CI config if we touch this.
+cargo install --git https://github.com/rust-lang/rust-semverver --rev 71c340ff867d2f79613cfe02c6714f1d2ef00bc4
 
 TARGETS=
 case "${OS}" in