Merge pull request SuperMap#229 from SuperMap/dependabot/npm_and_yarn/pngjs-6.0.0

Bump pngjs from 5.0.0 to 6.0.0

Author: songyumeng

package.json

@@ -96,7 +96,7 @@
     "mock-socket": "^9.0.3",
     "nightwatch": "^1.4.3",
     "open": "^7.3.0",
-    "pngjs": "^5.0.0",
+    "pngjs": "^6.0.0",
     "pre-commit": "^1.2.2",
     "request": "^2.88.0",
     "selenium-server": "3.141.59",