Pin nightly build to 2020-05-09

#115

Author: dtolnay

.github/workflows/ci.yml

@@ -12,7 +12,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable]
+        rust:
+            # pinned due to https://github.com/serde-rs/serde-rs.github.io/issues/115
+          - nightly-2020-05-09
+          - beta
+          - stable
     steps:
       - uses: actions/checkout@v2
       - uses: dtolnay/rust-toolchain@master