Weekly release v0.2.8: better diagnostics and condition simplifications

Summary:
Major commits include:
* Change error message when evaluating PossiblyNormalCompletion
* Added --omitInvariants option to prevent invariants from being included in generated code.
* Print out call stack in default error handler
* More simplifications
* Add missing check for invalid use of Map
* Simplify if conditions

Reviewed By: cblappert

Differential Revision: D5965959

fbshipit-source-id: e8eb8e053d9a121d2b4de352658269a5ec856f43

package.json

@@ -1,6 +1,6 @@
 {
   "name": "prepack",
-  "version": "0.2.8-alpha.0",
+  "version": "0.2.8",
   "description": "Execute a JS bundle, serialize global state and side effects to a snapshot that can be quickly restored.",
   "homepage": "https://github.com/facebook/prepack",
   "repository": {