bump typescript (coz it doesn't build with old)

Author: devanshj

package.json

@@ -41,7 +41,7 @@
     "rimraf": "^2.6.2",
     "ts-jest": "^23.0.0",
     "tslint": "^5.10.0",
-    "typescript": "~2.8.2"
+    "typescript": "^3.9.6"
   },
   "dependencies": {
     "antlr4ts": "^0.4.1-alpha.0"

yarn.lock

@@ -3526,9 +3526,10 @@ type-check@~0.3.2:
   dependencies:
     prelude-ls "~1.1.2"
 
-typescript@~2.8.2:
-  version "2.8.4"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.8.4.tgz#0b1db68e6bdfb0b767fa2ab642136a35b059b199"
+typescript@^3.9.6:
+  version "3.9.6"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.6.tgz#8f3e0198a34c3ae17091b35571d3afd31999365a"
+  integrity sha512-Pspx3oKAPJtjNwE92YS05HQoY7z2SFyOpHo9MqJor3BXAGNaPUs83CuVp9VISFkSjyRfiTpmKuAYGJB7S7hOxw==
 
 uglify-js@^2.6:
   version "2.8.29"