This will make a fraction of a single percent of a difference. Please do not worry any longer. Things much bigger than this (the quality of the argument in your writing sample, your grades, your personal statement, your test scores, your recommendations) will determine whether you get in or not.
That's assuming that they will even notice it. I'm not in English, but if it's anything at all like the sciences, they'll be looking at the writing, and only glance at the references to make sure that they're there. In any case, I've seen such typos in published articles.
I should point out that when you're referring to an unnamed university, as opposed to a named university ("applying to a university" vs. "Harvard University") the word "university" is not capitalized. That led me to suspect you were not a native speaker, but really your English is excellent for a non-native speaker. I think they will be impressed by your English rather than otherwise. Please attempt to worry about something else.
I would not have suspected that you are not a native English speaker had you not mentioned it. Considering that this is how you write for a forum, I suspect that the English on your application is even better, and I would also be surprised if the program is not impressed by this.
If you want to worry about something, think about employment prospects for English PhD's...
Good luck!