Disbled line wrapping in Harbor example base64 command

Disabled the line wrapping in encoding of the credentials.
The default behavior of the base64 command is wrapping after 76 chars.
If the credential is longer than that it causes the following error
during the next command.

/kaniko/.docker/config.json: invalid character '\n' in string literal

doc/user/project/integrations/harbor.md

@@ -75,7 +75,7 @@ docker:
     entrypoint: ['']
   script:
     - mkdir -p /kaniko/.docker
-    - echo "{\"auths\":{\"${HARBOR_HOST}\":{\"auth\":\"$(echo -n ${HARBOR_USERNAME}:${HARBOR_PASSWORD} | base64)\"}}}" > /kaniko/.docker/config.json
+    - echo "{\"auths\":{\"${HARBOR_HOST}\":{\"auth\":\"$(echo -n ${HARBOR_USERNAME}:${HARBOR_PASSWORD} | base64 -w 0)\"}}}" > /kaniko/.docker/config.json
     - >-
       /kaniko/executor
       --context "${CI_PROJECT_DIR}"