PHP has various language constructs such as [[http://php.net/manual/en/function.echo.php | echo]] and [[http://php.net/manual/en/function.require.php | require]] which can be called with or without parentheses. For example, `echo "Foo";` and `echo("Foo");` are equivalent. We should add a linter rule to `ArcanistXHPASTLinter` which favors the parenthesis being omitted.