Only run bench on master. Update criterion version

.github/workflows/bench.yml

@@ -0,0 +1,21 @@
+name: Benchmark
+
+on:
+  push:
+    branches:
+      - master
+    tags-ignore:
+      - "v*"
+
+jobs:
+  bench:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - run: cargo bench --bench main -- --output-format bencher | tee crates/flowistry/benches/output.txt
+      - uses: benchmark-action/github-action-benchmark@v1
+        with:
+          tool: 'cargo'
+          output-file-path: crates/flowistry/benches/output.txt
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          auto-push: true

crates/flowistry/Cargo.toml

@@ -29,7 +29,7 @@ html-escape = {version = "0.2", optional = true}
 [dev-dependencies]
 # Hack based on https://github.com/rust-lang/cargo/issues/2911
 flowistry = { path = ".", features = ["test"] }
-criterion = "0.4"
+criterion = "0.5.1"
 env_logger = {version = "0.9", default-features = false}
 test-log = "0.2"
 glob = "0.3.0"