vfs: fix proxyvfs inheritance
The proxyvfs class is designed to overwrite some of the vfs logic. Yet, it did
not use normal class inheritance. This is becoming an issue as `abstractvfs`
method could take precedence over their `proxyvfs` version.
We fix the inheritance chain to be as expected.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}