Add missing expand=False for v2.18.3 (#8342)

Installing the current version of Picard fails with:

```
==> Error: Unable to parse extension from https://github.com/broadinstitute/picard/releases/download/2.18.3/picard.jar.

If this URL is for a tarball but does not include the file extension
in the name, you can explicitly declare it with the following syntax:

    version('1.2.3', 'hash', extension='tar.gz')

If this URL is for a download like a .jar or .whl that does not need
to be expanded, or an uncompressed installation script, you can tell
Spack not to expand it with the following syntax:

    version('1.2.3', 'hash', expand=False)
```

Fix it, but adding `expand=False`, like the other versions.

0 files changed, 0 insertions, 0 deletions