Cordova安装camera插件是提示CAMERA_USAGE_DESCRIPTION, PHOTOLIBRARY_USAGE_DESCRIPTION变量没找到

现象：

Installing "cordova-plugin-camera" for ios
Failed to install 'cordova-plugin-camera':Error: Variable(s) missing: CAMERA_USAGE_DESCRIPTION, PHOTOLIBRARY_USAGE_DESCRIPTION
    at /usr/local/lib/node_modules/cordova/node_modules/cordova-lib/src/plugman/install.js:304:23
    at _fulfilled (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:787:54)
    at self.promiseDispatch.done (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:816:30)
    at Promise.promise.promiseDispatch (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:749:13)
    at /usr/local/lib/node_modules/cordova/node_modules/q/q.js:557:44
    at flush (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:108:17)
    at process._tickCallback (node.js:442:13)
    at Function.Module.runMain (module.js:499:11)
    at startup (node.js:119:16)
    at node.js:929:3
Error: Variable(s) missing: CAMERA_USAGE_DESCRIPTION, PHOTOLIBRARY_USAGE_DESCRIPTION
    at /usr/local/lib/node_modules/cordova/node_modules/cordova-lib/src/plugman/install.js:304:23
    at _fulfilled (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:787:54)
    at self.promiseDispatch.done (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:816:30)
    at Promise.promise.promiseDispatch (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:749:13)
    at /usr/local/lib/node_modules/cordova/node_modules/q/q.js:557:44
    at flush (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:108:17)
    at process._tickCallback (node.js:442:13)
    at Function.Module.runMain (module.js:499:11)
    at startup (node.js:119:16)
    at node.js:929:3

解决办法：

cordova plugin add cordova-plugin-camera --variable CAMERA_USAGE_DESCRIPTION="my usage message" --variable PHOTOLIBRARY_USAGE_DESCRIPTION="my usage message"