Fix error 'Unsupported platform for fsevents' by making optional

Signed-off-by: Jan-Christoph Borchardt <hey@jancborchardt.net>

package-lock.json

@@ -7411,7 +7411,7 @@
       "version": "2.0.7",
       "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.0.7.tgz",
       "integrity": "sha512-a7YT0SV3RB+DjYcppwVDLtn13UQnmg0SWZS7ezZD0UjnLwXmy8Zm21GMVGLaFGimIqcvyMQaOJBrop8MyOp1kQ==",
-      "dev": true
+      "optional": true
     },
     "fstream": {
       "version": "1.0.12",

package.json

@@ -91,7 +91,6 @@
 		"eslint-plugin-standard": "^4.0.1",
 		"eslint-plugin-vue": "^5.2.3",
 		"file-loader": "^4.2.0",
-		"fsevents": "^2.0.7",
 		"jest": "^24.9.0",
 		"jest-serializer-vue": "^2.0.2",
 		"node-sass": "^4.12.0",
@@ -108,6 +107,9 @@
 		"webpack-cli": "^3.3.7",
 		"webpack-merge": "^4.2.1"
 	},
+	"optionalDependencies": {
+		"fsevents": "^2.0.7"
+	},
 	"jest": {
 		"moduleFileExtensions": [
 			"js",