I get error when trying to build android package on ionicframework.com

npm run build success
$ cordova platform add android --no-fetch
WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
Using cordova-fetch for cordova-android@6.4.0
Adding android project…
Creating Cordova project for the Android platform:
Path: platforms/android
Package: io.ionic.starter
Name: worktocloud
Activity: MainActivity
Android target: android-26
Subproject Path: CordovaLib
Android project created with cordova-android@6.4.0
Discovered plugin “cordova-plugin-whitelist” in config.xml. Adding it to the project
Installing “cordova-plugin-whitelist” for android

           This plugin is only applicable for versions of cordova-android greater than 4.0. If you have a previous platform version, you do *not* need this plugin since the whitelist will be built in.

Adding cordova-plugin-whitelist to package.json
Saved plugin info for “cordova-plugin-whitelist” to config.xml
Discovered plugin “cordova-plugin-device” in config.xml. Adding it to the project
Installing “cordova-plugin-device” for android
Adding cordova-plugin-device to package.json
Saved plugin info for “cordova-plugin-device” to config.xml
Discovered plugin “cordova-plugin-splashscreen” in config.xml. Adding it to the project
Installing “cordova-plugin-splashscreen” for android
Adding cordova-plugin-splashscreen to package.json
Saved plugin info for “cordova-plugin-splashscreen” to config.xml
Discovered plugin “cordova-plugin-ionic-keyboard” in config.xml. Adding it to the project
Installing “cordova-plugin-ionic-keyboard” for android
Adding cordova-plugin-ionic-keyboard to package.json
Saved plugin info for “cordova-plugin-ionic-keyboard” to config.xml
Discovered plugin “WebViewer” in config.xml. Adding it to the project
Failed to restore plugin “WebViewer” from config.xml. You might need to try adding it again. Error: Failed to fetch plugin WebViewer@~0.0.1 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 1 Error output:
npm ERR! code E404
npm ERR! 404 Not Found: WebViewer@~0.0.1

npm ERR! A complete log of this run can be found in:
npm ERR! /home/gitlab-runner/.npm/_logs/2018-09-29T13_48_00_642Z-debug.log
Discovered plugin “cordova-plugin-ionic” in config.xml. Adding it to the project
Installing “cordova-plugin-ionic” for android
Plugin dependency “cordova-plugin-splashscreen@5.0.2” already fetched, using that version.
Dependent plugin “cordova-plugin-splashscreen” already installed on android.
Installing “cordova-plugin-ionic-webview” for android
Subproject Path: CordovaLib
Installing “cordova-plugin-file” for android

The Android Persistent storage location now defaults to “Internal”. Please check this plugin’s README to see if your application needs any changes in its config.xml.

If this is a new application no changes are required.

If this is an update to an existing application that did not specify an “AndroidPersistentFileLocation” you may need to add:

  ""

to config.xml in order for the application to find previously stored files.

Installing “cordova-plugin-file-transfer” for android
Plugin dependency “cordova-plugin-file@6.0.1” already fetched, using that version.
Dependent plugin “cordova-plugin-file” already installed on android.
Adding cordova-plugin-ionic to package.json
Saved plugin info for “cordova-plugin-ionic” to config.xml
–save flag or autosave detected
Saving android@~6.4.0 into config.xml file …
cordova platform add android --no-fetch failed
Running after script…
$ run “clean-up”