correct param in docker_linux.go for memory.stat
correct param in docker_linux.go for memory.stat

The version of docker on Ubuntu18.04 and Centos7 are old, and the
parameters in memory.stat on Ubuntu18.04 and Centos7 are as following:

cat /sys/fs/cgroup/memory/docker/33f962ca254969762d750ced9a97d8deef67535b96b1e8c17abd0939a3f2cbcf/memory.stat

cache 1110016
rss 413696
rss_huge 0
shmem 0
mapped_file 1015808
dirty 0
writeback 0
pgpgin 1610
pgpgout 1238
pgfault 1923
pgmajfault 12
inactive_anon 262144
active_anon 151552
inactive_file 0
active_file 1110016
unevictable 0
hierarchical_memory_limit 9223372036854771712
total_cache 1110016
total_rss 413696
total_rss_huge 0
total_shmem 0
total_mapped_file 1015808
total_dirty 0
total_writeback 0
total_pgpgin 1610
total_pgpgout 1238
total_pgfault 1923
total_pgmajfault 12
total_inactive_anon 262144
total_active_anon 151552
total_inactive_file 0
total_active_file 1110016
total_unevictable 0

this patch is for backward.

influxdb/gopsutil,influxdb/gopsutil