hghave: update rustfmt criterion
In 9ebc10ad4a04 I updated `rustfmt` without touching hghave, which means
that the CI has been skipping the format test ever since. Thankfully, only
one offending line exists in the code that's been introduced since.
Differential Revision: https://phab.mercurial-scm.org/D12180
{
// 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)
}