ignore VmFlags field when reading /proc/<pid>/smaps

Fix gopsutil parsing error on recent kernel smaps
```text
00400000-0040e000 r-xp 00000000 fd:09 297                                /bin/cat
Size:                 56 kB
Rss:                  56 kB
Pss:                  28 kB
Shared_Clean:         56 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:           56 kB
Anonymous:             0 kB
AnonHugePages:         0 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:                0 kB
VmFlags: rd ex mr mw me dw 
```