Bugfix(typescript) pin typescript@3.6.4 for @ts-ignore support in jsx

Use of `@ts-ignore` in jsx expressions is unsupported. Somehow it works
anyway in typescript@3.6.4 so we need to pin until we've resolved the
ignore comments.

Example of unsupported comment:

```
{ /*
  // @ts-ignore something
  */ }
```

see microsoft/TypeScript#31147

app/package.json

@@ -171,7 +171,7 @@
     "relay-compiler-language-typescript": "^10.1.0",
     "relay-test-utils": "^7.0.0",
     "require-context.macro": "^1.2.2",
-    "typescript": "^3.6.4",
+    "typescript": "3.6.4",
     "webpack": "^4.41.0",
     "xo": "^0.25.0"
   },

app/yarn.lock

@@ -13408,10 +13408,10 @@ typedarray@^0.0.6:
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
   integrity sha1-hnrHTjhkGHsdPUfZlqeOxciDB3c=
 
-typescript@^3.6.4:
-  version "3.7.2"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.7.2.tgz#27e489b95fa5909445e9fef5ee48d81697ad18fb"
-  integrity sha512-ml7V7JfiN2Xwvcer+XAf2csGO1bPBdRbFCkYBczNZggrBZ9c7G3riSUeJmqEU5uOtXNPMhE3n+R4FA/3YOAWOQ==
+typescript@3.6.4:
+  version "3.6.4"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.6.4.tgz#b18752bb3792bc1a0281335f7f6ebf1bbfc5b91d"
+  integrity sha512-unoCll1+l+YK4i4F8f22TaNVPRHcD9PA3yCuZ8g5e0qGqlVlJ/8FSateOLLSagn+Yg5+ZwuPkL8LFUc0Jcvksg==
 
 ua-parser-js@^0.7.18:
   version "0.7.20"