When testing rustc 1.36, use compatible dependencies.

The latest versions of `ppv-lite86` and `libc` don't compile with
`rustc` 1.36.  When testing with `rustc` 1.36, use the last compatible
version of the dependencies.

Author: nwalfield

.github/workflows/test.yml

@@ -78,6 +78,13 @@ jobs:
           cargo test --target ${{ matrix.target }} --benches --features=nightly
           cargo test --target ${{ matrix.target }} --manifest-path rand_distr/Cargo.toml --benches
           cargo test --target ${{ matrix.target }} --lib --tests --no-default-features --features min_const_gen
+      - name: Update Cargo.lock 1.36
+        if: ${{ matrix.toolchain == '1.36.0' }}
+        run: |
+          cargo update
+          # Last version of some packages that compile with 1.36
+          cargo update -p ppv-lite86 --precise 0.2.17
+          cargo update -p libc --precise 0.2.164
       - name: Test rand
         run: |
           cargo test --target ${{ matrix.target }} --lib --tests --no-default-features