Utilise load-grunt-tasks.

Gruntfile.js

 const readdirp = require("readdirp");
+const loadGruntTasks = require("load-grunt-tasks");
 const {
   extname,
   dirname,
@@ -102,11 +103,7 @@ module.exports = grunt => {
     clean: ["dist/**"]
   });
 
-  grunt.loadNpmTasks("grunt-contrib-clean");
-  grunt.loadNpmTasks("grunt-contrib-copy");
-  grunt.loadNpmTasks("grunt-exec");
-  grunt.loadNpmTasks("grunt-http-server");
-  grunt.loadNpmTasks("grunt-watcher");
+  loadGruntTasks(grunt, { pattern: ["grunt-*"] });
 
   grunt.registerTask("default", ["build"]);
   grunt.registerTask("serve", ["http-server", "build:dev", "watcher"]);

package.json

@@ -30,9 +30,10 @@
     "reveal.js": "git+https://gitlab.irstea.fr/guillaume.perreal/reveal.js.git#irstea"
   },
   "devDependencies": {
-    "prettier": "^6.5.1",
     "husky": "^1.3.1",
-    "lint-staged": "^8.2.1"
+    "lint-staged": "^8.2.1",
+    "load-grunt-tasks": "^5.1.0",
+    "prettier": "^6.5.1"
   },
   "husky": {
     "pre-commit": "lint-staged"