chore(issuer): add heroku

Author: Fahd

packages/polymath-issuer/Procfile

@@ -1 +1 @@
-web: cd packages/polymath-issuer && yarn start
+web: cd packages/polymath-issuer && yarn start:prod

packages/polymath-issuer/package.json

@@ -7,11 +7,11 @@
     "node": ">=8.9"
   },
   "scripts": {
-    "start": "serve -s build",
+    "start": "node scripts/start.js",
+    "start:prod": "serve -s build",
     "build": "node scripts/build.js",
     "test": "node ./scripts/test.js --env=jsdom",
-    "typecheck": "flow --show-all-branches",
-    "heroku-postbuild": "npm run build"
+    "typecheck": "flow --show-all-branches"
   },
   "dependencies": {
     "@babel/runtime": "7.0.0",