ci+docs: CentOS renamed the PowerTools repo to lowercase

Change-Id: I3868d1763c5b9d060603e440627ad8990de3ae4e

.jenkins.d/00-deps.sh

@@ -34,7 +34,7 @@ elif has Ubuntu $NODE_LABELS; then
     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

INSTALL.md

@@ -22,7 +22,7 @@ This document describes how to build and install ndn-tools.
 
     On CentOS and Fedora:
 
-        sudo dnf config-manager --enable PowerTools  # CentOS only
+        sudo dnf config-manager --enable powertools  # CentOS only
         sudo dnf install libpcap-devel
 
 ## Build Steps