Handle internal as a keyword too

Author: Wilfred

hack-mode.el

@@ -600,7 +600,8 @@ If PROPERTIZE-TAGS is non-nil, apply `hack-xhp-tag' to tag names."
      "final" "finally" "for" "foreach" "function" "global" "goto" "if"
      "implements" "include" "include_once" "insteadof"
      "interface" "is" "isset" "list" "namespace" "new" "parent"
-     "print" "private" "protected" "public" "require" "require_once"
+     "print" "private" "protected" "public" "internal"
+     "require" "require_once"
      "return" "self" "static" "switch" "throw" "trait"
      "try" "unset" "use" "var" "while"
      "yield"