Updated Ghost versioning lib to include all prerelease IDs

- currently if Ghost has a version of something like
  `3.37.0-pre.abc.def`, Ghost will return `3.37.0-pre.abc` as the full
  version
- this hides parts of the version which are useful for debugging
- this commit updates the logic to join together all prerelease elements
  so we keep the full string

core/server/lib/ghost-version.js

@@ -8,7 +8,7 @@ let _private = {};
 _private.compose = function compose(type) {
     switch (type) {
     case 'pre':
-        return plainVersion + '-' + semver.prerelease(version)[0] + (semver.prerelease(version)[1] ? '.' + semver.prerelease(version)[1] : '');
+        return plainVersion + '-' + semver.prerelease(version).join('.');
     default:
         return version;
     }