update: Updated typescript type specifications to use browser entry point (#754)

## Summary
Some application were having a hard time finding `http` module being used in the node entry point. Changed the type specifications to point to browser entry point.

## Test plan
All existing tests pass

## Issues
#686

Author: zashraf1985

packages/optimizely-sdk/package.json

@@ -6,7 +6,7 @@
   "main": "dist/optimizely.node.min.js",
   "browser": "dist/optimizely.browser.min.js",
   "react-native": "dist/optimizely.react_native.min.js",
-  "typings": "dist/index.node.d.ts",
+  "typings": "dist/index.browser.d.ts",
   "scripts": {
     "clean": "rm -rf dist",
     "lint": "tsc --noEmit && eslint 'lib/**/*.js' 'lib/**/*.ts'",