refactor: upgrade JsonParser use (away from deprecated method)

Author: stevebillings

src/main/java/com/synopsys/integration/blackduck/imageinspector/image/docker/manifest/DockerManifest.java

@@ -109,8 +109,7 @@ private List<DockerImageInfo> getManifestContents() throws IOException {
         logger.debug("getManifestContents(): extracting manifest file content");
         final String manifestContentString = extractManifestFileContent();
         logger.trace(String.format("getManifestContents(): parsing: %s", manifestContentString));
-        final JsonParser parser = new JsonParser();
-        final JsonArray manifestContent = parser.parse(manifestContentString).getAsJsonArray();
+        final JsonArray manifestContent = JsonParser.parseString(manifestContentString).getAsJsonArray();
         final Gson gson = new Gson();
         for (final JsonElement element : manifestContent) {
             logger.trace(String.format("getManifestContents(): element: %s", element.toString()));