安装activiti插件时，总是安装不上，会报出错误，{Cannotcompletetheinstallbecauseoneormorerequireditemscouldnotbefound.Softwarebeinginstalled:ActivitiEclipseBPMN2.0Designer5.18.0.201508100929(org.activiti.designer.feature.feature.group5.18.0.201508100929)Missingrequirement:ActivitiEclipseBPMN2.0Designer5.18.0.201508100