Put version into quotes, otherwise it fails

When using the `zsh` shell, the command fails because of:

```
$ composer create-project symfony/framework-standard-edition myproject/ ~2.5
zsh: no such user or named directory: 2.5
```

This problem does not occur in Bash.
Quoting the version number does not effect Bash, and fixes ZSH.
minor #4091 Put version into quotes, otherwise it fails in ZSH (dannykopping)

This PR was merged into the 2.5 branch.

Discussion
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Put version into quotes, otherwise it fails in ZSH

When using the `zsh` shell, the command fails because of:

```
$ composer create-project symfony/framework-standard-edition myproject/ ~2.5
zsh: no such user or named directory: 2.5
```

This problem does not occur in `bash`.
Quoting the version number does not effect `bash`, and fixes `zsh`.

Commits
-------

6dc62a8 Put version into quotes, otherwise it fails