Fix Erlang/OTP 20.0 / 20.1 compilation

* Proposed fix for #636
* Bumped into the issue with the Ubuntu 18.04 Erlang/OTP package using 20.2.
  Travis doesn't appear to have 20.2 but does have 20.1.7
  (https://docs.travis-ci.com/user/languages/erlang/#otprelease-versions).

Author: okeuday

.travis.yml

@@ -3,6 +3,7 @@ otp_release:
   - 22.1
   - 22.0
   - 21.3
+  - 20.1.7
 
 env:
   - TEST=1

rebar.config

@@ -6,7 +6,7 @@
             {platform_define, "^[0-9]+", namespaced_types},
             {platform_define, "^R", no_proxy_sni_support},
             {platform_define, "^(19)|(20)", no_customize_hostname_check},
-            {platform_define, "^20", buggy_chacha_ciphers}
+            {platform_define, "^20\.3", buggy_chacha_ciphers}
            ]}.
 
 {erl_first_files,