procfs 0.9.x cause panic on linux which version number greater than 255

[DCjanus]

procfs 0.9.x assume numbers in Linux kernel version is small than 256, and parse text from '/proc/sys/kernel/osrelease' to three u8

And since Linux has been release a version which patch version is 256, this line in procfs 0.9.x would panic.

In the last release of this lib(0.12.0), we are still using the procfs 0.9.x, which would cause panic, if my Linux version number greater than 255.

ref: eminence/procfs#137
ref: #408

[DCjanus]

This change is import to some people, please release a new version.

[lucab]

Release PR at #415.