Update app-distribution.md

[Light13008]

a typo was corrected, 'webapps' was changed to 'web app'.

Please describe what your Pull Request does

A change was committed in file site/en/enterprise/app-distribution.md

A clear and concise description of what your Pull Request does.

Please tag each issue this Pull Request resolves
#416
Add transform for webapp->web app #416

• Resolves #
  Typo was resolved in the documentation in file
  site/en/enterprise/app-distribution.md

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.