ci+docs: CentOS renamed the PowerTools repo to lowercase

Change-Id: I4b78986f3af17d2124824992e31b408ebe8de03a
diff --git a/.jenkins.d/00-deps.sh b/.jenkins.d/00-deps.sh
index 67ac9ae..0e81bf9 100755
--- a/.jenkins.d/00-deps.sh
+++ b/.jenkins.d/00-deps.sh
@@ -34,7 +34,7 @@
     fi
 
 elif has CentOS-8 $NODE_LABELS; then
-    sudo dnf config-manager --enable PowerTools
+    sudo dnf config-manager --enable powertools
     sudo dnf -y install gcc-c++ libasan pkgconf-pkg-config python3 \
                         boost-devel openssl-devel sqlite-devel \
                         libpcap-devel systemd-devel