fix: restore the author metadata that npm drops from the package

package.json declared the author as an array:

    "author": ["Michael Martinez", "Helmut Dersch"]

npm does not accept an array there. `author` names one person, and
`contributors` is the array. npm therefore dropped the field, and the published
2.2.0 carries no author at all:

    $ npm view @cornerstonejs/jpeg-lossless-decoder-js author --json
    {}

So the package lost the attribution to the two people who wrote the decoder.
The unscoped jpeg-lossless-decoder-js has the same defect, and this fork
inherited it.

Both names are kept, in the shape npm reads:

    "author": "Michael Martinez",
    "contributors": ["Helmut Dersch"]

Michael Martinez wrote the JavaScript port and the selection value 2 to 7
support; Helmut Dersch wrote the original Java decoder. README.md's
acknowledgments section is the source for both.

Verified: `npm pkg get` normalizes the manifest to a string author and a
contributors array, the packed tarball's package.json carries both, the lint
passes and all 54 tests pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: wayfarer3130

package.json

@@ -51,8 +51,8 @@
     "1.2.840.10008.1.2.4.57",
     "1.2.840.10008.1.2.4.70"
   ],
-  "author": [
-    "Michael Martinez",
+  "author": "Michael Martinez",
+  "contributors": [
     "Helmut Dersch"
   ],
   "license": "MIT",