config.md: make the version a semver
config.md: make the version a semver

As suggested in #15 make this a semver so we have some interpretation of
compatibility.

zenlinTechnofreak/specs,LK4D4/specs,HardikDR/specs,vishh/specs,jhjeong-kr/specs,gao-feng/specs,jonboulle/specs,dustymabe/specs,marcosnils/specs,ujuc/specs,laijs/specs,hqhq/runtime-spec,haijunTan/specs,talwai/specs,kensipe/specs,hqhq/specs,cloudfoundry-incubator/specs,wangkirin/specs,ChengTiesheng/specs,wking/opencontainer-specs,opencontainers/specs,runcom/specs,wking/opencontainer-runtime-spec,rootfs/specs,opencontainers/runtime-spec,vbatts/specs,navidshaikh/specs,sladage/specs,philips/specs,mheon/specs