Fix example.rules typos.
Thanks for spotting those
instance:node_cpus:count = count(node_cpu{mode="idle"}) without (cpu,mode)
# CPU in use by CPU.
-instance_cpu:node_cpu_not_idle:rate5m = sum rate(node_cpu{mode!="idle"}[5m])) without (mode)
+instance_cpu:node_cpu_not_idle:rate5m = sum(rate(node_cpu{mode!="idle"}[5m])) without (mode)
# CPU in use by mode.
-instance_mode:node_cpu:rate5m = sum rate(node_cpu[5m])) without (cpu)
+instance_mode:node_cpu:rate5m = sum(rate(node_cpu[5m])) without (cpu)
