Updated travis.yml to remove PHP 7.2 and run tests against PHP 7.3 and 7.4.

Updated readme.md to display PHP version support.

Author: hexydec

.travis.yml

@@ -1,7 +1,10 @@
 language: php
 
 php:
-  - '7.2'
   - '7.3'
+  - '7.4'
 
 script: phpunit --bootstrap src/autoload.php --verbose --coverage-text --coverage-clover=coverage.xml tests
+
+after_success:
+    - bash <(curl -s https://codecov.io/bash)

readme.md

@@ -62,6 +62,10 @@ if ($doc->open($url) {
 - [About Document Recycling](docs/recycling.md)
 - [Object Performance](docs/performance.md)
 
+## Support
+
+HTMLdoc supports PHP version 7.3+.
+
 ## Contributing
 
 If you find an issue with HTMLdoc, please create an issue in the tracker.