[release] v1.26.0 - Exposure callback and spec update bug fix (#201)

### New Features
  - New options to pass in ExposureCallback and IncludeDisabledExposures
  ### Fixes
- Fixes a bug where we could update the internal store with stale values
(older than the current values in memory). While this was unlikely, now
it wont happen





>Included In This Release
>- 048e42f kat-statsig
>   - only throw away spec if lcut is older (#200)
>- 1c2f343 kat-statsig
>   - exposure callback (#197)
>- 2e30520 kat-statsig
>   - check lcut before process (#198)

statsig_metadata.go

@@ -14,7 +14,7 @@ type statsigMetadata struct {
 func getStatsigMetadata() statsigMetadata {
 	return statsigMetadata{
 		SDKType:         "go-sdk",
-		SDKVersion:      "v1.25.0",
+		SDKVersion:      "v1.26.0",
 		LanguageVersion: runtime.Version()[2:],
 		SessionID:       SessionID(),
 	}