Bump pngjs from 3.4.0 to 4.0.0

Bumps [pngjs](https://github.com/lukeapage/pngjs2) from 3.4.0 to 4.0.0.
- [Release notes](https://github.com/lukeapage/pngjs2/releases)
- [Commits](https://github.com/lukeapage/pngjs2/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package-lock.json

@@ -9555,6 +9555,14 @@
       "dev": true,
       "requires": {
         "pngjs": "^3.4.0"
+      },
+      "dependencies": {
+        "pngjs": {
+          "version": "3.4.0",
+          "resolved": "https://registry.npmjs.org/pngjs/-/pngjs-3.4.0.tgz",
+          "integrity": "sha512-NCrCHhWmnQklfH4MtJMRjZ2a8c80qXeMlQMv2uVp9ISJMTt562SbGd6n2oq0PaPgKm7Z6pL9E2UlLIhC+SHL3w==",
+          "dev": true
+        }
       }
     },
     "pixelworks": {
@@ -9581,9 +9589,9 @@
       }
     },
     "pngjs": {
-      "version": "3.4.0",
-      "resolved": "https://registry.npmjs.org/pngjs/-/pngjs-3.4.0.tgz",
-      "integrity": "sha512-NCrCHhWmnQklfH4MtJMRjZ2a8c80qXeMlQMv2uVp9ISJMTt562SbGd6n2oq0PaPgKm7Z6pL9E2UlLIhC+SHL3w==",
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/pngjs/-/pngjs-4.0.0.tgz",
+      "integrity": "sha512-607/ROF2oFEQoL+cQD894iYHdZhXWB8lISaR4MWI8VUgHPViC7FODcIySWCdnkkdrVD4YrfVU8Rmd6ZlMkq8Pw==",
       "dev": true
     },
     "portfinder": {

package.json

@@ -87,7 +87,7 @@
     "mocha": "7.1.1",
     "ol-mapbox-style": "^6.1.1",
     "pixelmatch": "^5.1.0",
-    "pngjs": "^3.4.0",
+    "pngjs": "^4.0.0",
     "proj4": "2.6.1",
     "puppeteer": "~2.1.0",
     "rollup": "^2.1.0",