Rework grep.sh
Rework grep.sh

I noticed that `grep.sh' didn't work correctly for explorer source code and
decided that it's better to use version which doesn't require enumerating all
folders.
Initially it was proposed by @sectore and I slightly modified it.

input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl