feat: upgrade pngjs from 3.4.0 to 7.0.0

Snyk has created this PR to upgrade pngjs from 3.4.0 to 7.0.0.

See this package in npm:
pngjs

See this project in Snyk:
https://app.snyk.io/org/okeamah/project/4d0b68ad-fe61-43e4-99f2-11eb5f2c9063?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -6,7 +6,7 @@
   "dependencies": {
     "@types/node": "^10.12.12",
     "chalk": "^2.4.1",
-    "pngjs": "^3.3.3",
+    "pngjs": "^7.0.0",
     "ts-lint": "^4.5.1",
     "ts-node": "^7.0.1",
     "typescript": "^3.2.2"