[PHP client] Fix README.md template for php

[okapon]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.
  @jebentier (2017/07) @dkarlovi (2017/07) @mandrean (2017/08) @jfastnacht (2017/09) @ackintosh (2017/09) @ybelenko (2018/07)

Description of the PR

I fixed README.mustache template for php.

There is a problem with the php client's Installation & Usage section.

Please see composer documentation bellow.
https://getcomposer.org/doc/05-repositories.md#loading-a-package-from-a-vcs-repository

[wing328]

The VCS driver to be used is detected automatically based on the URL. However, should you need to specify one for whatever reason, you can use git-bitbucket, hg-bitbucket, github, gitlab, perforce, fossil, git, svn or hg as the repository type instead of vcs.

Thanks for the PR. I agree vcs is a better choice.

[ackintosh]

Nice catch. ✨

[okapon]

Thank you very much ✨

[wing328]

@okapon thanks for the PR, which has been included in the v3.3.4 release: https://twitter.com/oas_generator/status/1068772409795207168

[okapon]

@wing328 Thank you for letting me know 😄