Update required version to 4.80

4.64 is no longer compatible, and 4.80 is the oldest supported version
that is newer than 4.64.

Author: fredemmott

.github/workflows/build-and-test.yml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         os: [ ubuntu , macos ]
         hhvm:
-          - 4.64
+          - 4.80
           - latest
           - nightly
     runs-on: ${{matrix.os}}-latest

composer.json

@@ -4,7 +4,7 @@
   "license": "MIT",
   "keywords": ["hack", "TypeAssert"],
   "require": {
-    "hhvm": "^4.64",
+    "hhvm": "^4.80",
     "hhvm/hsl": "^4.0"
   },
   "extra": {