misc: Use bash's command instead of which

Bash has a built-in command, `command`, that will search the path and
return the full path to a command if it exists (or an exit code of 1 if
it does not), preventing the requirement of the `which` package.

test/test-yamlfmt.sh

@@ -17,7 +17,7 @@ set -o pipefail
 
 ROOT=$(dirname "${BASH_SOURCE}")/..
 
-RUBY=`which ruby 2>/dev/null`
+RUBY=`command -v ruby 2>/dev/null`
 if [ -z $RUBY ]; then
 	fail_test "The 'ruby' utility can't be found."
 fi