README.md: Add missing 'time' import to example
README.md: Add missing 'time' import to example

zj8487/go-cache,nothingmuch/go-cache,patrickmn/go-cache,cognusion/go-cache-lru,ggaaooppeenngg/cachemap,pmylund/go-cache,jiangjin/go-cache,yxd-hde/go-cache