Drop legacy HHVM support due to lack of support and failing test suite

.github/workflows/ci.yml

@@ -43,16 +43,3 @@ jobs:
       - run: composer require symfony/console:^3.0 --dry-run --working-dir=tests/install-as-dep
         if: ${{ matrix.php >= 5.5 && matrix.php < 8.0 }}
       - run: composer install --dry-run --working-dir=tests/install-as-dep
-
-  PHPUnit-hhvm:
-    name: PHPUnit (HHVM)
-    runs-on: ubuntu-18.04
-    continue-on-error: true
-    steps:
-      - uses: actions/checkout@v2
-      - uses: azjezz/setup-hhvm@v1
-        with:
-          version: lts-3.30
-      - run: hhvm $(which composer) install
-      - run: hhvm vendor/bin/phpunit
-      - run: hhvm $(which composer) install --dry-run --working-dir=tests/install-as-dep

README.md

@@ -74,9 +74,8 @@ $ php graph-composer.phar export ~/path/to/your/project
 You can grab a copy of clue/graph-composer in either of the following ways.
 
 This project aims to run on any platform and thus does not require any PHP
-extensions and supports running on legacy PHP 5.3 through current PHP 7+ and
-HHVM.
-It's *highly recommended to use PHP 7+* for this project.
+extensions and supports running on legacy PHP 5.3 through current PHP 8+.
+It's *highly recommended to use the latest supported PHP version* for this project.
 
 The graph drawing feature is powered by the excellent [GraphViz](https://www.graphviz.org)
 software. This means you'll have to install GraphViz (`dot` executable).