plugins: add testing-library types

plugins/home-page/package.json

@@ -11,6 +11,7 @@
     "@testing-library/user-event": "^7.1.2",
     "@types/jest": "^24.0.0",
     "@types/node": "^12.0.0",
+    "@types/testing-library__jest-dom": "5.0.2",
     "react": "^16.12.0",
     "react-dom": "^16.12.0",
     "@material-ui/core": "^4.9.1",

plugins/welcome/package.json

@@ -12,7 +12,8 @@
   },
   "devDependencies": {
     "@spotify-backstage/core": "^0.1.0",
-    "@spotify-backstage/cli": "^0.1.0"
+    "@spotify-backstage/cli": "^0.1.0",
+    "@types/testing-library__jest-dom": "5.0.2"
   },
   "dependencies": {
     "@material-ui/lab": "4.0.0-alpha.45"