wkwebview-engine-localhost not installable

> cordova create wkwvtest my.project.id wkwvtest
> cd wkwvtest/
> cordova platform add ios@4
(have to do it two times .. initially i get the Message "Error: Failed to fetch platform cordova-ios@4
Probably this is either a connection problem, or platform spec is incorrect.
Check your connection and platform name/version/URL.
Failed to get absolute path to installed module")
> cordova plugin add https://github.com/apache/cordova-plugins.git#wkwebview-engine-localhost
Results in
Failed to install 'cordova-labs-wkwebview-engine-localhost': CordovaError: Failed to fetch plugin https://git-wip-us.apache.org/repos/asf/cordova-plugins.git#local-webserver via registry.
Probably this is either a connection problem, or plugin spec is incorrect.
Check your connection and plugin name/version/URL.
Error: npm: Command failed with exit code 254 Error output:
npm ERR! not a package /var/folders/p_/ffn44cb97ssfrcvsd77yfvdm0000gn/T/npm-8251-0ea75174/git-wip-us.apache.org/repos/asf/cordova-plugins.git/local-webserver
npm ERR! Darwin 16.5.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "https://git-wip-us.apache.org/repos/asf/cordova-plugins.git#local-webserver" "--save"
npm ERR! node v5.1.1
npm ERR! npm v3.3.12
npm ERR! path /var/folders/p_/ffn44cb97ssfrcvsd77yfvdm0000gn/T/npm-8251-0ea75174/unpack-f36d6fc4f98995f590a09a46396a0443/package.json
npm ERR! code ENOENT
npm ERR! errno -2
npm ERR! syscall open

npm ERR! enoent ENOENT: no such file or directory, open '/var/folders/p_/ffn44cb97ssfrcvsd77yfvdm0000gn/T/npm-8251-0ea75174/unpack-f36d6fc4f98995f590a09a46396a0443/package.json'
npm ERR! enoent This is most likely not a problem with npm itself
npm ERR! enoent and is related to npm not being able to find a file.
npm ERR! enoent

npm ERR! Please include the following file with any support request:
npm ERR! /Users/volkergraf/DEV/NODE/Carfinder/wkwvtest/wkwvtest/node_modules/npm-debug.log
at /usr/local/lib/node_modules/cordova/node_modules/cordova-lib/src/plugman/fetch.js:205:33
at _rejected (/usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:864:24)
at /usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:890:30
at Promise.when (/usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:1142:31)
at Promise.promise.promiseDispatch (/usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:808:41)
at /usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:624:44
at runSingle (/usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:137:13)
at flush (/usr/local/lib/node_modules/cordova/node_modules/cordova-fetch/node_modules/q/q.js:125:13)
at doNTCallback0 (node.js:430:9)
at process._tickCallback (node.js:359:13)
Error: Failed to fetch plugin https://git-wip-us.apache.org/repos/asf/cordova-plugins.git#local-webserver via registry.
Probably this is either a connection problem, or plugin spec is incorrect.
Check your connection and plugin name/version/URL.
Error: npm: Command failed with exit code 254 Error output:
npm ERR! not a package /var/folders/p_/ffn44cb97ssfrcvsd77yfvdm0000gn/T/npm-8251-0ea75174/git-wip-us.apache.org/repos/asf/cordova-plugins.git/local-webserver
npm ERR! Darwin 16.5.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "https://git-wip-us.apache.org/repos/asf/cordova-plugins.git#local-webserver" "--save"
npm ERR! node v5.1.1
npm ERR! npm v3.3.12
npm ERR! path /var/folders/p_/ffn44cb97ssfrcvsd77yfvdm0000gn/T/npm-8251-0ea75174/unpack-f36d6fc4f98995f590a09a46396a0443/package.json
npm ERR! code ENOENT
npm ERR! errno -2
npm ERR! syscall open

npm ERR! enoent ENOENT: no such file or directory, open '/var/folders/p_/ffn44cb97ssfrcvsd77yfvdm0000gn/T/npm-8251-0ea75174/unpack-f36d6fc4f98995f590a09a46396a0443/package.json'
npm ERR! enoent This is most likely not a problem with npm itself
npm ERR! enoent and is related to npm not being able to find a file.
npm ERR! enoent

npm ERR! Please include the following file with any support request:
npm ERR! /Users/volkergraf/DEV/NODE/Carfinder/wkwvtest/wkwvtest/node_modules/npm-debug.log ..

Any Ideas ?