[whatwg] pushState / replaceState nits

[Justin Lebar]

In section 6.10.2:

"The pushState(data, title, url) method adds a state object to the
history." perhaps should be "... adds a state object *entry* to the
history."

"The replaceState(data, title, url) method updates the current entry
in the history to have a state object." perhaps should be
"The replaceState(data, title, url) method adds a stateObject to the
current history entry or modifies (updates?) the entry's stateObject."

"When either of these methods are invoked" should be "When either of
these methods is invoked".

-Justin