Upgrade devDeps to resolve security warnings

CHANGELOG.md

@@ -160,3 +160,6 @@ Released with 1.0.0-beta.37 code base.
 - Add missing subscription.on('connected') TS type definition (#3319)
 - Add missing bignumber.js dependency for TS types (#3386)
 - Upgrade swarm-js to 0.1.40 to remove npm vulnerability warning (#3399)
+- Upgrade devDeps to resolve security warnings
+  - dtslint 0.4.2 => 3.4.1
+  - definitelytyped-header-parser 1.0.1 => 3.9.0

package.json

@@ -139,7 +139,7 @@
         "puppeteer": "^1.20.0",
         "sandboxed-module": "^2.0.3",
         "surge": "^0.21.3",
-        "typescript": "next",
+        "typescript": "^3.8.3",
         "underscore": "^1.9.1",
         "vinyl-source-stream": "^2.0.0",
         "wait-port": "^0.2.6",