Zerif-lite header Section Menu

I am using Zerif lite theme. My header has a logo and main menu(5 items)
When I resize the screen, menu is shifted to second line…increasing the menu bar height.
and when i resize window to 767px…hamburger menu is displayed.

What I want:
I want to display hamburger menu to be displayed instead of main menu going to second line.
Please help me to do the same.
Thanks for the help..