ci: migrate to GitHub Actions

Due to the recent changes to the Travis CI platform (see [1]), we will
now use GitHub Actions to run the tests.

Note: the certificate was updated because it failed with newer Node.js versions

```
_tls_common.js:129
      c.context.setCert(cert);
                ^

Error: error:140AB18F:SSL routines:SSL_CTX_use_certificate:ee key too small
    at Object.createSecureContext (_tls_common.js:129:17)
    at Server.setSecureContext (_tls_wrap.js:1328:27)
```

Reference: https://docs.github.com/en/free-pro-team@latest/actions/guides/building-and-testing-java-with-maven

[1]: https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing

src/test/java/io/socket/client/SSLConnectionTest.java

@@ -66,7 +66,7 @@ public class SSLConnectionTest extends Connection {
         TrustManagerFactory tmf = TrustManagerFactory.getInstance("SunX509");
         tmf.init(ks);
 
-        SSLContext sslContext = SSLContext.getInstance("TLSv1");
+        SSLContext sslContext = SSLContext.getInstance("TLS");
         sslContext.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);
 
         sOkHttpClient = new OkHttpClient.Builder()

src/test/resources/cert.pem

@@ -1,10 +1,21 @@
 -----BEGIN CERTIFICATE-----
-MIIBfDCCASYCCQDTnGd/oOyF1DANBgkqhkiG9w0BAQUFADBFMQswCQYDVQQGEwJB
-VTETMBEGA1UECBMKU29tZS1TdGF0ZTEhMB8GA1UEChMYSW50ZXJuZXQgV2lkZ2l0
-cyBQdHkgTHRkMB4XDTE0MDcwNzEzMTUzN1oXDTQxMTEyMTEzMTUzN1owRTELMAkG
-A1UEBhMCQVUxEzARBgNVBAgTClNvbWUtU3RhdGUxITAfBgNVBAoTGEludGVybmV0
-IFdpZGdpdHMgUHR5IEx0ZDBcMA0GCSqGSIb3DQEBAQUAA0sAMEgCQQC6sdeFPlqk
-5Pap9woFx1RO05gLidw4MNcL+ZRSxy/sNeE4PhT/RLFcEvnXiHc92wT8YB5Z+WCM
-k/jRQ0q19PNPAgMBAAEwDQYJKoZIhvcNAQEFBQADQQCnmm1N/yZiMBZw2JDfbsx3
-ecc0BGQ2BwWQuGHzP07TMi1AuOyNZSczl907OphYb9iRC8shZ4O+oXjQAuGTQ1Hp
+MIIDazCCAlOgAwIBAgIUPRxvTroGehqqXb8XOvqliIcKyagwDQYJKoZIhvcNAQEL
+BQAwRTELMAkGA1UEBhMCQVUxEzARBgNVBAgMClNvbWUtU3RhdGUxITAfBgNVBAoM
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+HwYDVQQKDBhJbnRlcm5ldCBXaWRnaXRzIFB0eSBMdGQwggEiMA0GCSqGSIb3DQEB
+AQUAA4IBDwAwggEKAoIBAQCxJ8fUV6sRiNub3Af6jGpGTsWpCqtxBkRSADENMzdT
+Twz4wUXXbgv/Tbt3XJovR1RtE9nx+WyA4XqBdfr8s/qDLiVWiyszU9E6jBjQva9B
+aGJDZU0BEXjGDTFaE4tL3E/YWZvXVKmrEiq0aZa6anbjOefjG46CnXgfir/TZlx+
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+dleQ4HGxxA8FTTAPBgNVHRMBAf8EBTADAQH/MA0GCSqGSIb3DQEBCwUAA4IBAQB8
+8Jjqcipf2jHdiRx+4ltJ5y4hitgPsPRsR74L22hHAvICFC+2b2Iu3R1vSBJj5140
+HwwH7LUPyt3IKzQP8EOB2MbZsfH10Z3/ChnH1MHmOCDO+Wusi0C0HaOfWp/rAsgY
+q+wLMGd3G72/Ba1YdaGHm9SjrziyAEnF5Uz8sUkQrDbZTiWp35PagJTDhdQ6pnUh
+JROaoYgNYhGjQ89V1geIpIVTVqoGvLyvAi4k58KQyMUtxi7IEG/IdgopZAL9IL75
+D7fMXi21mrb1ohJpk3JlS1Z1XtoynIs4uzlv9wg6yKU5ExZ0QsUwuBekopUuSAvg
+XeFIZbJz/WoAo0ZJ6o8Y
 -----END CERTIFICATE-----

src/test/resources/key.pem

@@ -1,9 +1,28 @@
------BEGIN RSA PRIVATE KEY-----
-MIIBOwIBAAJBALqx14U+WqTk9qn3CgXHVE7TmAuJ3Dgw1wv5lFLHL+w14Tg+FP9E
-sVwS+deIdz3bBPxgHln5YIyT+NFDSrX0808CAwEAAQJAIdwLSIEsk2drTRwe1zl1
-ku5RTxZruE0zU1qqifDSQjab1StAK1tapxBVRlRlyLCfD704UClsU8sjGtq0Nh6n
-kQIhAO2YJM1g0w9bWYet3zC2UdEASPzaQ7llpZmc51NRBx2NAiEAyShICAaclEuy
-wwuD4hibV+b6I8CLYoyPBo32EaceN0sCIQCUed6NxfM/houlgV+Xtmfcnzv9X3yx
-EDdzjpz08Q7sRQIgZFv1fBOYYSBXQppnJRFzx2pUmCvDHtrTrMh84RfIqnsCIQCf
-JjNXXxOaHn1PNZpi6EHReiFQmy1Swt+AxpTsKixsfA==
------END RSA PRIVATE KEY-----
+-----BEGIN PRIVATE KEY-----
+MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQCxJ8fUV6sRiNub
+3Af6jGpGTsWpCqtxBkRSADENMzdTTwz4wUXXbgv/Tbt3XJovR1RtE9nx+WyA4XqB
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+QDcKANSWBfa5XyxtbhF+McutcgBlwWHW/I6EyisCgYAnJ35YgVEx4hakXQNSwlPR
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+2oxN1xfkQYQ9cLYTAOfrDw==
+-----END PRIVATE KEY-----