added apache 2 license file
added apache 2 license file

brandur/gojsonschema,lylex/gojsonschema,juju/gojsonschema,stephensearles/gojsonschema,mickep76/gojsonschema,pki-io/gojsonschema,cristiangraz/gojsonschema,slapresta/gojsonschema,xeipuuv/gojsonschema,realglobe-Inc/gojsonschema,sanathb/gojsonschema,xyliuke/gojsonschema