ci: switch to shallow cloning of 'wrk' repository

.circleci/install-wrk.sh

@@ -6,8 +6,8 @@ cd "$(dirname "$0")"
 
 cd /tmp/
 sudo apt-get install build-essential libssl-dev git -y
-git clone https://github.com/wg/wrk.git wrk
+git clone --depth=1 https://github.com/wg/wrk.git wrk
 cd wrk
 sudo make
 # move the executable to somewhere in your PATH, ex:
-sudo cp wrk /usr/local/bin
+sudo cp wrk /usr/local/bin