ci+docs: CentOS renamed the PowerTools repo to lowercase

Change-Id: I3868d1763c5b9d060603e440627ad8990de3ae4e
diff --git a/INSTALL.md b/INSTALL.md
index a4a325c..8e0cd24 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -22,7 +22,7 @@
 
     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