Target 2.15 and 2.16 (#48)

* Target 2.15 and 2.16

* Adds back Cross.toml

Author: tzumby

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        nif: ["2.16", "2.15", "2.14"]
+        nif: ["2.16", "2.15"]
         job:
           - { target: arm-unknown-linux-gnueabihf , os: ubuntu-20.04 , use-cross: true }
           - { target: aarch64-unknown-linux-gnu   , os: ubuntu-20.04 , use-cross: true }

native/exkeccak/Cross.toml

@@ -0,0 +1,4 @@
+[build.env]
+passthrough = [
+  "RUSTLER_NIF_VERSION"
+]