.jshintrc

typing: add a couple of assertions to lrucachedict to help pytype

Fixes the following warnings:

    line 1488, in pop: No attribute 'markempty' on None [attribute-error]
         In Optional[Union[Any, _lrucachenode, nothing]]
    line 1578, in popoldest: No attribute 'markempty' on None [attribute-error]
         In Optional[Union[Any, _lrucachenode, nothing]]

Differential Revision: https://phab.mercurial-scm.org/D7674

{
    // 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)
}