Updating install.sh to change the repo used for ctrlp

Kein seems to have disappeared and the ctrlp.vim project from him has stagnated. There is an active fork under  https://github.com/ctrlpvim/ctrlp.vim  as a result of issue 591 ( https://github.com/kien/ctrlp.vim/issues/591 ). I propose switching to that instead.
Merge pull request #348 from timc3/patch-1

Updating install.sh to change the repo used for ctrlp