fix cpuUsage parser for linux

I found on systems where the top command presented CPU levels as Cpu(s) the ignorecase setting was not respected.

In testing, I found that replacing IGNORECASE with toupper resolved the parser.

Tested with procps-ng 3.3.12 on arm64 and amd64.

root@d3128d68ca51:/opt/shinobi# top -v
  procps-ng 3.3.12

top - 13:26:55 up 3 days, 21:09,  0 users,  load average: 18.89, 15.12, 13.88
Tasks:  16 total,   3 running,   9 sleeping,   0 stopped,   4 zombie
%Cpu(s): 64.4 us, 27.6 sy,  0.0 ni,  5.5 id,  0.0 wa,  1.2 hi,  1.3 si,  0.0 st
KiB Mem :  4056788 total,   226764 free,  1134340 used,  2695684 buff/cache
KiB Swap:        0 total,        0 free,        0 used.  2688924 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                                                           
19411 root      20   0  583280  92016  28944 R  61.4  2.3   2:03.03 ffmpeg                                                                                                                                            
19412 root      20   0  245956  47964  27404 R  51.5  1.2   1:34.90 ffmpeg                                                                                                                                            
19380 root      20   0  579188  84764  29156 S  49.1  2.1   1:43.44 ffmpeg

root@d3128d68ca51:/opt/shinobi# top -b -n 2 | awk '{IGNORECASE = 1} /^.?CPU/ {gsub("id,","100",$8); gsub("%","",$8); print 100-$8}' | tail -n 1

root@d3128d68ca51:/opt/shinobi# top -b -n 2 | awk 'toupper($0) ~ /^.?CPU/ {gsub("id,","100",$8); gsub("%","",$8); print 100-$8}' | tail -n 1
95.2