ci+docs: CentOS renamed the PowerTools repo to lowercase

Change-Id: I4b78986f3af17d2124824992e31b408ebe8de03a
diff --git a/docs/INSTALL.rst b/docs/INSTALL.rst
index d555476..a326ff3 100644
--- a/docs/INSTALL.rst
+++ b/docs/INSTALL.rst
@@ -107,7 +107,7 @@
 
   .. code-block:: sh
 
-    sudo dnf config-manager --enable PowerTools  # on CentOS only
+    sudo dnf config-manager --enable powertools  # on CentOS only
     sudo dnf install libpcap-devel systemd-devel
 
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