Set typescript to beta

Author: rrdelaney

package.json

@@ -31,7 +31,7 @@
     "source-map-support": "^0.5.6",
     "tslib": "1.11",
     "tslint": "5.11.0",
-    "typescript": "3.8.2"
+    "typescript": "^4.0.0-dev.20200429"
   },
   "scripts": {
     "build": "bazel build //:npm_package",

yarn.lock

@@ -1208,10 +1208,10 @@ tsutils@^2.27.2:
   dependencies:
     tslib "^1.8.1"
 
-typescript@3.8.2:
-  version "3.8.2"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.8.2.tgz#91d6868aaead7da74f493c553aeff76c0c0b1d5a"
-  integrity sha512-EgOVgL/4xfVrCMbhYKUQTdF37SQn4Iw73H5BgCrF1Abdun7Kwy/QZsE/ssAy0y4LxBbvua3PIbFsbRczWWnDdQ==
+typescript@^4.0.0-dev.20200429:
+  version "4.0.0-dev.20200429"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.0.0-dev.20200429.tgz#8af7f4e8aca5e91bb7cfef69b4ba96b3deedf4f3"
+  integrity sha512-r5LFE13k+4K3Zw2YNa30McHp4EtQzGTibFBib7yQWkO6oNftBlwEzgHcX2+KBA1S1FI0uZEoUOuo6l82R5sYgA==
 
 uglify-js@^3.1.4:
   version "3.6.0"