.travis.yml in tpm-key_attestation-0.4.0 vs .travis.yml in tpm-key_attestation-0.5.0

@@ -7,10 +7,9 @@
   - ruby-head
   - 2.7.0
   - 2.6.5
   - 2.5.7
   - 2.4.9
-  - 2.3.8
 
 gemfile:
   - gemfiles/openssl_head.gemfile
   - gemfiles/openssl_2_1.gemfile
   - gemfiles/openssl_2_0.gemfile