Add funding link to libvips' Open Collective

package.json

@@ -110,7 +110,7 @@
     "detect-libc": "^1.0.3",
     "nan": "^2.14.0",
     "npmlog": "^4.1.2",
-    "prebuild-install": "^5.3.2",
+    "prebuild-install": "^5.3.3",
     "semver": "^6.3.0",
     "simple-get": "^3.1.0",
     "tar": "^5.0.5",
@@ -120,12 +120,12 @@
     "async": "^3.1.0",
     "cc": "^1.0.2",
     "decompress-zip": "^0.3.2",
-    "documentation": "^12.1.2",
+    "documentation": "^12.1.3",
     "exif-reader": "^1.0.3",
     "icc": "^1.0.0",
     "license-checker": "^25.0.1",
     "mocha": "^6.2.2",
-    "mock-fs": "^4.10.2",
+    "mock-fs": "^4.10.3",
     "nyc": "^14.1.1",
     "prebuild": "^9.1.1",
     "prebuild-ci": "^3.1.0",
@@ -139,6 +139,9 @@
   "engines": {
     "node": ">=8.5.0"
   },
+  "funding": {
+    "url": "https://opencollective.com/libvips"
+  },
   "semistandard": {
     "env": [
       "mocha"