tools: Remove redundant grep -v vendors/ (#1996)

* tools: Remove redundant grep -v vendors/

This was used in conjunction with `go list <path>`, however `go list`
already ignores the vendor directory. This made this `grep -v` redundant.

* Missed an apostrophe

test/test_cover.sh

@@ -1,6 +1,6 @@
 #! /bin/bash
 
-PKGS=$(go list github.com/tendermint/tendermint/... | grep -v /vendor/)
+PKGS=$(go list github.com/tendermint/tendermint/...)
 
 set -e