upgrade to TypeScript 3.5.0 (dev) to fix readonly bug

Fix at microsoft/TypeScript#30734 for an issue with TypeScript 3.4.x and use of `readonly T[]`, which causes webpack to report the following error:

```
TypeError: Cannot read property 'instantiations' of undefined
```

Author: sqs

package.json

@@ -175,7 +175,7 @@
     "tslint": "^5.15.0",
     "tslint-language-service": "^0.9.9",
     "typedoc": "^0.14.0",
-    "typescript": "^3.4.1",
+    "typescript": "3.5.0-dev.20190406",
     "utc-version": "^1.1.0",
     "webpack": "^4.28.2",
     "webpack-dev-server": "^3.1.13",

yarn.lock

@@ -14735,15 +14735,20 @@ typedoc@^0.14.0:
     typescript "3.2.x"
 
 [email protected]:
-  version "3.2.2"
-  resolved "https://registry.npmjs.org/typescript/-/typescript-3.2.2.tgz#fe8101c46aa123f8353523ebdcf5730c2ae493e5"
-  integrity sha512-VCj5UiSyHBjwfYacmDuc/NOk4QQixbE+Wn7MFJuS0nRuPQbof132Pw4u53dm264O8LPc2MVsc7RJNml5szurkg==
+  version "3.2.4"
+  resolved "https://registry.npmjs.org/typescript/-/typescript-3.2.4.tgz#c585cb952912263d915b462726ce244ba510ef3d"
+  integrity sha512-0RNDbSdEokBeEAkgNbxJ+BLwSManFy9TeXz8uW+48j/xhEXv1ePME60olyzw2XzUqUBNAYFeJadIqAgNqIACwg==
 
-[email protected], typescript@^3.4.1:
+[email protected]:
   version "3.4.1"
   resolved "https://registry.npmjs.org/typescript/-/typescript-3.4.1.tgz#b6691be11a881ffa9a05765a205cb7383f3b63c6"
   integrity sha512-3NSMb2VzDQm8oBTLH6Nj55VVtUEpe/rgkIzMir0qVoLyjDZlnMBva0U6vDiV3IH+sl/Yu6oP5QwsAQtHPmDd2Q==
 
+[email protected]:
+  version "3.5.0-dev.20190406"
+  resolved "https://registry.npmjs.org/typescript/-/typescript-3.5.0-dev.20190406.tgz#9beda156dc682c342574796fa1212e13f5d0de2d"
+  integrity sha512-yBCj+5+CYlR+9tCP9IG784gcacpYNFNEQpXtwzONk7YonzT0KXn6qp2UhqpwKyJi0QC2f73k2LuVAsNwa/UXnA==
+
 ua-parser-js@^0.7.18:
   version "0.7.19"
   resolved "https://registry.npmjs.org/ua-parser-js/-/ua-parser-js-0.7.19.tgz#94151be4c0a7fb1d001af7022fdaca4642659e4b"