Drop support for OTP 18 and 19

They started to fail in CI. With 20 -> 28 we still get a nice coverage as far
back as 2017.

Author: nickva

.github/workflows/ci.yml

@@ -29,19 +29,6 @@ jobs:
       - run: make test
       - run: make edoc
       - run: REBAR=rebar make test
-  test-eol:
-    name: test ${{matrix.otp}} on ${{matrix.os}}
-    runs-on: ${{matrix.os}}
-    container:
-      image: erlang:${{matrix.otp}}
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-          - ubuntu-latest
-        otp:
-          - "19"
-          - "18"
     steps:
       # The old containers can't run checkout@v4
       - uses: actions/checkout@v3

rebar.config

@@ -1,7 +1,7 @@
 % -*- mode: erlang -*-
 {erl_opts, [debug_info,
-            {platform_define, "^(18|19|20|21|22)", new_crypto_unavailable},
-            {platform_define, "^(18|19|20)", ssl_handshake_unavailable},
+            {platform_define, "^(20|21|22)", new_crypto_unavailable},
+            {platform_define, "^20", ssl_handshake_unavailable},
             {platform_define, "^21-", otp_21}]}.
 {cover_enabled, true}.
 {eunit_opts, [verbose, {report,{eunit_surefire,[{dir,"."}]}}]}.