Use postgraphile@next and update some other deps

All deps have been tested and work fine with serverless deploys

Author: kalepail

package.json

@@ -13,14 +13,13 @@
   "dependencies": {
     "aws-serverless-express": "^3.3.5",
     "cors": "^2.8.5",
-    "pg": "7.4.1",
-    "postgraphile": "v4.2",
-    "postgraphile-core": "^4.2.0"
+    "pg": "^7.9.0",
+    "postgraphile": "^4.4.0-beta.9"
   },
   "devDependencies": {
-    "aws-sdk": "^2.389.0",
+    "aws-sdk": "^2.437.0",
     "serverless-content-encoding": "^1.1.0",
-    "webpack": "4.17.2",
-    "webpack-cli": "3.1.0"
+    "webpack": "4.29.6",
+    "webpack-cli": "3.3.0"
   }
 }