Fix typedoc prepare script to use npm

Reason: typedoc has package.lock, and yarn install would not install locked
dependencies but the newest one, hence breaking on newer packages than
the ones that actually work being pulled

package.json

@@ -61,7 +61,7 @@
   },
   "homepage": "https://github.com/cardano-foundation/ledgerjs-hw-app-cardano",
   "scripts": {
-    "prepare": "cd node_modules/typedoc && yarn install && yarn build",
+    "prepare": "cd node_modules/typedoc && npm install && npm run build",
     "prepack": "yarn build:flowtypes && yarn flow",
     "lint": "yarn eslint . --max-warnings=0",
     "clean": "rm -rf dist/",