prep for releases (optimizely#741)

prep for releases (optimizely#741)

revert optimizely#735 and prep for release 0.9.3 for `js-sdk-datafile…

…-manager` and 0.9.4 for `js-sdk-event-processor` (optimizely#739)

## Summary
React native dependencies were converted from `peer` to `optional` in `js-sd-datafile-manager` version `0.9.2` and `js-sdk-event-processor` version `0.9.3`. After releasing, it appeared that they did not work as expected. This PR reverts back that change which was made in optimizely#735 and updates changelog and npm version to make new releases for both the packages.

## Test plan
- Manually tested.
- All unit tests pass

revert optimizely#735 and prep for release 0.9.3 for `js-sdk-datafile…

…-manager` and 0.9.4 for `js-sdk-event-processor` (optimizely#739)

## Summary
React native dependencies were converted from `peer` to `optional` in `js-sd-datafile-manager` version `0.9.2` and `js-sdk-event-processor` version `0.9.3`. After releasing, it appeared that they did not work as expected. This PR reverts back that change which was made in optimizely#735 and updates changelog and npm version to make new releases for both the packages.

## Test plan
- Manually tested.
- All unit tests pass

chore: prep for release 0.9.2 for `js-sdk-datafile-manager` and 0.9.3…

… for `js-sdk-event-processor` (optimizely#738)

chore: prep for release 0.9.2 for `js-sdk-datafile-manager` and 0.9.3…

… for `js-sdk-event-processor` (optimizely#738)

chore: prep for release 4.9.1 (optimizely#734)

chore: prepare for release 4.9.0 (optimizely#731)

chore: Prep for release 4.8.0 (optimizely#726)

fix(Event Processor): impression event attributes exp, var should be …

…empty instead of null (optimizely#718)

## Summary
- experimentId and variationId should be empty if no variation or experiment is found.

## Test plan
- Manually tested
- All tests pass